Panel background configuration

Options to set background color and/or image
Custom font color handling. Fixes #101.
Make the lxqtmount-qt5 required only when building the mount plugin.

It was always required. Closes lxde#363.
Reorganize panel configuration dialog
Renames the translations source files

Renames it from xxxxx.ts.src to xxxxx.ts
Uses the new translations cmake modules
Moves translations from the local to the translations dir

We don't look there anymore.
Fixes translations generation

Closes lxde/lxqt-panel#367.
Fix draggind action from main menu
Get rid of Xlib on the keyboard indicator

Done using KGuiAddons's KModifierInfo
More info: http://api.kde.org/frameworks-api/frameworks5-apidocs/kguiaddons/html/classKModifierKeyInfo.html
Cancel widget move on panel with esc
Add time-only formats, improve popup in plugin-worldclock
Sort plugins alphabetically, remove non-existing plugin-helloworld
Update Russian translation
Plugin name fixed. Fixes #382
Merge branch 'master' of git.lxde.org:/lxde/lxqt-panel
Commit from LXDE Pootle server by user DanWin.: 294 of 305 strings translated (0 need review).
Merge branch 'master' of git.lxde.org:/lxde/lxqt-panel
Commit from LXDE Pootle server by user DanWin.: 305 of 305 strings translated (0 need review).
Add KDevelop project file type to .gitignore