Improve the Referrers > Overview report #3619

This is a proposal to improve the Referers > Overview report.

This will greatly increase the "at a glance" analytics capability of Piwik.

The full Referrers Overview layout could be:
* Top graph showing total visits graph, and Direct entry visits line (currently only shows direct entry visits)
* Below "Referrer Type", display sparklines for each ref type
* The sparklines should be enhanced and display a % evolution from yester the start of the graph displayed above.

[SPARKLINE_IMAGE] 518 from websites (35% of visits) [icon_image] +15% over the period 

* '+15% over the period' has a tooltip that reads '156 visits on Nov 6th, 177 on Dec 6th: +15%'
* on click on sparkline the graph loads "All visits" line + the clicked sparkline's line. User can then unclick the "all visits" to hide the line. But it is good to show the relative value straight ahead to further help analysis.
* Add a link below the 4 sparklines that says "More sparklines"
* When clicked this link will display the current "Distinct Referrers by Referrer Type" section of extra sparklines. These are useful to have, just better hide them by default.
* These extra sparklines should be extended to contain the % evolution and have consistent style with other sparkline (except they wont show the relative % since it does not apply to these stats).
* Reuse the row evolution css styles and template code: http://piwik.org/wp-content/uploads/2012/06/Piwik-mobile-iOS-VS-Android.png
* Below sparklines is the 2 columns listing. Similarly to the Goals report which has a similar 2 column view.
~~* Left column: listing the following reports ~~
* Right column: ajax loading by default the "All Referers report"
~~* Loads in the right, the clicked report from left column. ~~
* The reports listed on the left are, in this order:
* All Referrers (new report see #1899) <-- This one is pre-displayed
* Referrers Overview (showing direct VS search VS websites VS campaigns)
* Keywords
* Websites
* Campaigns
* Social Media
* Search Engines
* The code tpl+js+css from the Goals overview template should be refactored and reused.

The Referrers Overview will be suited for analysis. Let's make the code generic as I think it will be put to good use: We could reuse such a style for other Overview reports (Visitors > Overview or Goals > Overview) if it works well.

(In [7839]) Refs #3619, several improvements/modifications to Referrers overview, including:

• Add Total referrer metrics to evolution graph which are always displayed.
• Added evolution percentage next to sparklines.
• Moved other sparklines (for distinct metrics) to smaller section that slides down.

Notes:

• Fixed bug in broadcast.js where '+' chars were removed when sanitizing query params.
• Moved multisites evolution & previous period calculating code to Piwik core.
• Added section-toggler-link code to common js code (CoreHome/misc.js).
• Refactored evolution percentage code used for row evolution popup.

(In [7841]) Refs #3619, commit missing file.

very good improvements! I'm going to commit some tweaks too.

In b202ff1f5483fd8fb523e82965444b8e87b7871d: Refs #3619

• Updating icons
• Tooltip more readable
• putting language in General and deprecating redundant translation

a7c4cf9d9c3b3a172acd30e07c68974826aa61e6 refs this ticket. Commit message below:

Refs #3619, refactor Goals 'conversions by type of visit' template/logic into reusable View in CoreHome.

Notes:

• Removed need for initial AJAX loading in new view.

In add95a5c2dacb3065a850a4b2a76e8d009347518: Fixes #3619, add reports by dimension section to Referrers overview.

Notes:

• fix bug in last #3619 commit that broke referrers overview page.

In 609579ed33cc6407c6b7e7aa0c224722ea238889: Refs #3619, fix bug where Overview header will be displayed even if there are 0 visits for the period.