display: remove unused code

[endlessm/eos-shell#3365]
display: fix GCC warnings

Unused function and missing const.

[endlessm/eos-shell#3365]
region: fix GCC warnings

We never use priv, but the whole function is also unused - just cut it.

[endlessm/eos-shell#3365]
universal-access: fix GCC warnings

[endlessm/eos-shell#3365]
display: Silence -Wmaybe-uninitialized

We create rotate_box only when show_rotation is TRUE, and the
conditions for checking the different kinds of rotation do not make
sense when show_rotation is FALSE.

https://bugzilla.gnome.org/show_bug.cgi?id=727023
display: refactor the setup dialog not to be synchronous

As we're going to be pre-selecting the output in the next commit, if
there's only one.

[endlessm/eos-shell#3365]
display: pre-select output if there's only one

Saves one click.

[endlessm/eos-shell#3365]
Merge pull request #14 from endlessm/shell/3365

Shell/3365