i3bar: fix resource leak: statusline_ctx needs to be freed first

In practice this is rarely noticeable, unless you very often switch
screen resolutions, I think.

fixes #1172
Merge branch 'fix-i3bar-leak'
Bugfix: ipc_receive_message reply leak

The function ipc_recv_message in libi3 allocates memory to the location
of the `message` reply in src/ipc_receive_message.c with malloc and must
be freed.

This memory leak was found using valgrind.
Merge branch 'fix-recv-memleak'
Merge branch 'master' into next
Improved detection of windows that want floating

Windows that match the following criteria are floated by default:
- dialog, utility, toolbar, or splash windows,
- modal windows, or
- windows that have specified equal minimum and maximum size.

closes #1182
Add test for floating types

Add a test that verifies that windows with properties that indicate they
should be floating are indeed opened floating.