bind mode color support, fix gtk3 check

bind mode color support and gtk3 check fix, thanks to @antoniotrkdz

Sort workspaces, helps with multi-monitor setups

Sorting the workspaces keeps the icons in order on multi-monitor setups. Thanks to @tott for the fix.

Python 3.5 support, custom foreground colors

This release re-adds support for Python 3.5. Recent changes inadvertently meant this applet required 3.6.

Tested using Python 3.5.2 on Ubuntu 16.04.

Also, thanks to @tott foreground color customizations are now supported.

Works with GTK 2 and GTK 3

Thanks to help from @landmaj , mate-i3-applet can now work in GTK 2 or GTK 3.

Switch to GTK 3.0

This release switchins to using GTK 3.0. This is a breaking change, hence the major bump.

You will need MATE versions 1.18.0 or greater.

If you are on an older GTK 2 based MATE (ie, older than 1.18.0), please use version 1.1.1 which is GTK 2 based. It's possible a future version of the applet may detect which version of GTK to use. But it's also possible it might not. To be honest, I don't have too much time to dedicate to this project unfortunately.

Fix regression on restart

Version 1.1.0 had a regression in it. I missed reconnected the subscriptions correctly on i3 restart.

This version fixes the regression.

Added mode label -- BAD RELEASE

This release had a regression, use 1.1.1 instead

This release adds a mode label. The most common mode is "resize", but any mode you use in i3 will show up.

Once you return to "default" mode, the label goes away.