Add hooks for context menus
work around linux crash on paste

https://anki.tenderapp.com/discussions/ankidesktop/2019-inaccessible-firewall-blocked-media-url-paste-hangs-anki-for-a-minute-until-a-network-is-unreachable-like-message-appears
Merge pull request #40 from steveaw/add-hooks3

Add hooks for context menus
escape + in deck names
warn when prefs.db corrupt and catch another case
remove filtered deck restriction on stats
allow includegraphics in latex
fix incorrect code that was not restoring clipboard
don't try to download local image urls