attempt to use gtk3
Revert "attempt to use gtk3"

This reverts commit 769105c59b94713674e09638fd5aaa0a27108883.
display new mail ico (first steps)
move linux-ish FiretrayChat.jsm to linux/.

We'll probably create a FiretrayChat.prototype when/if we support chat in
winnt.
* fix firetray's chat support policy handling
* implement windowGetAttention(), setIconImageDefault(), setIconImageNewMail()

At this stage, we must consider adapting the preferences' UI.
* creation of basic icon with text
* load .bmp in addition to .ico (and load them LR_SHARED)
* use ctypes pointer.isNull()