Add functionality in the installer to enable timezone and language
configuration.

Update semantics of what the "timezone" parameter actually is in this
context to make room for the actual timezone configuration.

Update the pip3 commands to instead use the safer "python3 -m pip"
method as some distros do not install pip3 as part of the python3-pip
install (but calling the pip module using python3 is almost a
guaranteed).

Few updates to files for formatting consistency (aesthetics).

(cherry picked from commit 72f43265b5)
Signed-off-by: Nico Rey <rey.nico@gmail.com>