Don't show loss of precision warning when only pasting point entities.
Add preference to toggle Alt+MMB to move camera.
If no drag can be started on mouse down, don't pick up objects on the way.
Add a preference option to enable Alt+MMB to move the mouse forward and backward.
Fix more precision problems with vertex correction and snapping.
Quickly detect duplicate planes when adding them to a brush.

Signed-off-by: Kristian Duske <kristian.duske@gmail.com>
Merge branch 'Release_1.0.0' of github.com:kduske/TrenchBroom into Release_1.0.0