Tb78

[antixn]

I'm a kee user and i was quite frustrated recently : during a few months i had thunderbird 68 and kee working again... and then TB78 came and broke stuff again...

@dlech I've seen your comment on the issue 30 and i've decided to give a hand. I've choosen to implement the upgrade to TB78 the quick way with the WindowListener API

My first target was to be able to debug it, it's not proper debug but the new target in the makefile launches the node app web-ext with the local plugin files and ease tries and tests.

The only functionnal element i was able to see working is the overload of the login popup providing the text "You are logged out of your database (it may be locked)". It guided me through the TB68, TB78 and helped me being sure that i wasn't breaking anything in the process. After the upgrade, as a sort of bonus i've also been able to see that the options page was also displaying "correctly"

I'm pretty sure a lot of string resources and management code could be removed (TB40) but i wanted to avoid making big changes as the objective here was mainly to allow kee to work with thunderbird 78. I would be interested to invest more time for the mail extension real upgrade but this PR seems quite enough for a first contact :)