Add standard stuff (AUTHORS, LICENSE...)
Add a proper install system

So, there were instructions on how to do a make install, but
there was no actual install script on CMakeLists.txt. Well,
now there is.

When make install, it will copy focus binary to bin/ folder.
There's also a desktop shortcut on data folder, it will be
copied to share/applications, for instance to add a shortcut
on application menu.

README and INSTALL were updated to reflect the fact that it's
a good idea to install on /usr instead of /usr/local to make
the software available to all users. Sometimes installing to
/usr/local has some issues. For instance, slingshot doesn't
show instantly shortcuts added to /usr/local/share/applications.
Save and restore window state using GSettings

A GSettings schema is implemented and window information such as
position, size or whether it's maximized or not is added. This
information is restored when Focus is opened and it's saved when
Focus closes.

This schema is likely to change in a future as I add more settings.

Please note that the schema has to be compiled before actually
using Focus in order to the application to properly work. If doing
a make install, it's automatically copied to schemas folder and
compiled. Else, you'll have to do it by yourself.

Saving and restoring state is one of the guidelines from the
ElementaryOS Project User Interface Guidelines.