Merge pull request #640 from luis-pereira/unify-desktop-plugin-widgets-name

razorqt-desktop: Unify plugins and widgets names. Closes #447
Removes hardcoded "Add plugin" window title

The "Add plugins" dialog is shared between the panel and the desktop. The
window title should be set by the calling code and not be hardcoded in the
dialog ui. I didn't realize that in my 107d8c3e76 commit.
We use setWindowTitle() to set the appropriate title.

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>
razorqt-panel/panel: Renames "Add plugins ..." to "Add Panel Widgets"

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>
Renames the "Add plugin" button to "Add Widget"

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>
razorqt-panel/panel: Use capitals for in menus and window titles

For the sake of consistency.

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>
razorqt-panel/panel: Replace "Delete Panel" by "Remove Panel"

Let's be consistent with the desktop module.

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>
razorqt-desktop: Remove "New" from "Add New Desktop Widget..." caption

Consistency once again.

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>