Fix Request: right mouse click Suppress / Details only correct on violation level

[jborgers]

Right mouse click menu shows on ruleset, rule and violation level, all for Suppress and Details.
Suppress only makes sense on violation level, on other levels it should not show (currently doesn't do anything on rule and ruleset, which is correct.)
Details only makes sense on violation and rule level, currently only works on violation level.

The tag in pmd.xml is called 'externalInfoUrl', maybe a better name for 'Details' is 'More info'.