pidgin/pidgin

Rename gtkstyle.[ch] to pidginstyle.[ch] and fix up the dark mode check.

2020-11-10, Gary Kramlich
559881c7bf92
Rename gtkstyle.[ch] to pidginstyle.[ch] and fix up the dark mode check.

Testing Done:
* Ran with arc-dark and adwatia.
* Stepped through the debugger to make sure it was detected right.
* Joined a muc with both themes, the colors change but there're impossible to see as most of that code is elsewhere and not addressed in this review request.
* Also noticed that nicks in mucs are doubled, not sure what, but it's that way with out this patch as well.

Reviewed at https://reviews.imfreedom.org/r/208/
#tab-label-typing {
color: #4e9a06;
}
#tab-label-typed {
color: #c4a000;
}
#tab-label-attention {
color: #006aff;
}
#tab-label-unreadchat {
color: #cc0000;
}
#tab-label-event {
color: #888a85;
}