Replicate the XWiki Cache feature from the community version

[iuliabalan]

See the "Flush JMX & XWiki Cache" feature of the Admin Tools community version: the "XWiki Cache" feature could be used to visualise the usage of the different caches, to check the statistics about the page cache. This feature is very useful (e.g when investigating performance issues) and would be nice to have it in the Pro version.

[petrenkonikita112263]

This functionality already exists in it since #31.

[oanat]

The functionality is only partially implemented because the most important part the display of caches info is actually missing.

[petrenkonikita112263]

In this case, UI already has link to xwiki.cfg file where that parameter can be seen.