o.c.display.pvtable: Add context menu command to select/de-select all.

Often, only a few channels should be restored. Now this is more
convenient by de-selecting all rows, then selecting those which should
be restored.
o.c.display.pvnames: Extenalize strings for (De-)Select actions
o.c.display.pvtable: Fixes for setting the 'tolerance'

If no row specific rows are selected to set their tolerance, the
tolerance for every row in the table will be updated.
When setting the tolerance, the table is marked as 'dirty' so the new
configuration can be saved.
o.c.display.pvtable: Mark table 'dirty' when item renamed
Merge pull request #294 from ControlSystemStudio/proj_pvtable_tweaks

Proj pvtable tweaks: Fixes #293