Removed the inclusion of some unneed Thunderbird DTDs, one of them
to be highly modified in version 30.0.
I was notified by Sebastian Hengst from Thunderbird about the change
and instructions to adapt the code and where to find proper localizable
strings.
But I'm not using any of that in current version, unlinked the files
and version bump to 0.7.3.
Added Dutch locale
Merge pull request #27 from oeekker/master

Added Dutch locale
Add underscore to tooltips to show accesskey
Add code for showing accesskey in tooltip when accesskey doesn't appear in tooltip
Update dutch accesskey for usw-sticky pin
Merge pull request #28 from oeekker/master

Add underscore to tooltips to show accesskey
Merge branch 'master' into issue12