When WITH_XC_NETWORKING is defined, create a QToolButton beside the Edit Entry -> Entry -> URL, which when pressed, acts as though the Edit Entry -> Icon -> Download Favicon button is pressed. This button is disabled (grayed-out) when the URL text is empty, and enabled when the text is present.
Fixes#936
* Add favicon download button
* Remove the progress dialog that appears when
downloading an entry's URL's favicon since (when working correctly) it disappears before it can be read. When downloading icons from the button
located next to the URL text box, display a message panel that confirms the download was a success.
* Do not show successful icon download msg if icon alread exists
* Support ! modifier (same as '-')
* Create reusable PopupHelpWidget as self-contained popup that can
be positioned around a parent widget and will follow the movement
and sizing of the window
* Eliminated KEEPASSXC_MAIN_WINDOW macro and replaced with
getMainWindow() function
* Add tests to cover search help show/hide
