Add minimum opacity setting for user-adjusted window opacity (mouse wheel and
keybindings)

Depends on cinnamon-desktop 8dacf5efad64038aefb2162e7bacbb1a080d7d7b
prevent draggable borders being non-existant after a monitor/screen/resolution
change.
Read minimum window opacity as a 0-100 value, convert it to 0-255.
Merge branch 'min-window-opacity' of https://github.com/mtwebster/muffin into mtwebster-min-window-opacity

Conflicts:
	src/core/prefs.c
Merge branch 'mtwebster-min-window-opacity'
2.2.4
Changed logic for detection of fullscreen legacy windows (fixes Chromium fullscreen issues)
2.2.5
Revert "Hide resize grip on gtk2/3 windows when the window is tiled - it makes"

This reverts commit 6f67cf3cd822111041756dd6fff97e94cd4f4c65.

This fixes the bug portion of: https://github.com/linuxmint/muffin/issues/151
keybindings: Fix wrong reaction to tiling hotkeys when a window is maximized.

Fixes #150
2.2.6
2.3.0