Visualize useful synthetic information when user clicks 'Tags'

When user clicks 'Tags', s\he opens a view which is remarkable for its lack of information about tags.

That place could be used to display some summary of the tags used which could be useful or interesting for most of the users.

Here is a modest proposal:

you are using 58 tags on 4678 objects.

The tagged objects have 2 tags on average.

The five most used tags are:

• one (704 times)
• two (578 times)
• three (550 time)
• four (489 times)
• five (265 times)

You are tagging mainly files (3921 objects), but you tag also contacts (400 objects), and calendar items (357 objects)

The last phrase is an extension that considers the possibility of an unified tag system ( see #13330 )

The text tries to provide a lot of info in a few lines. It shows

• basic information on how much you are using the tag tool
• the most used tags by you
• basic information on how you are using the tag tool

In case of interest, there are three main paths to expand this feature:

• display more generic information
• display information about the other users
• display specific information on a tag after the user selects it

No files, tests, or entry points are identified in the issue. Locate the Tags view and existing tag data aggregation, then clarify which summary is in scope; done should be a useful, compact tag-usage summary shown when the user opens Tags.