Add spell checker support to context menu

Fixes: GNOME/epiphany#181
3 jobs for 181 in 6 minutes and 11 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #348933
flatpak

00:04:17

 
  Deploy
passed #348934
review

00:01:08

failed #348935
allowed to fail manual
stop_review

00:00:45

 
Name Stage Failure
failed
stop_review Deploy
 * [new tag]         WEBKIT_BRANCHPOINT          -> WEBKIT_BRANCHPOINT
* [new tag] XULRUNNER_BRANCHPOINT -> XULRUNNER_BRANCHPOINT
* [new tag] actual-2.29.6 -> actual-2.29.6
* [new tag] gnome-2-8-branchpoint -> gnome-2-8-branchpoint
* [new tag] help -> help
* [new tag] pre-gnome-2-10-branchpoint -> pre-gnome-2-10-branchpoint
Checking out c398d645 as 181...
fatal: reference is not a tree: c398d645a0c9587ea17a31cfde7b33308977ec24
ERROR: Job failed: exit code 1