Installer tweaks - Prompt for camera during install

[linuxkidd]

Add camera selection to installer, pretty-up the reboot ask.

Resolves #682
Resolves #658

[EricClaeys]

Michael,
can the prompt for camera be the first thing the script does after printing the welcome message? I'm concerned that users may not see it or may not read it if it's at the end, after all the other output lines. It can edit config.sh later but would prompt earlier.

select_camera() should first check that ${ALLSKY_CONFIG}/config.sh exists rather than asking the user if it exists.
This might require limiting select_camera() to just prompting, then add update_camera() to do the update.

If you move "source variables.sh" to the top you can dump the lines that set the colors since that's done in variables.sh.

[linuxkidd]

Keep in mind, this is a full-screen takeover that forces the user to select an option.

However, I did move the camera selection to the top of the order of operations, and check for ${ALLSKY_CONFIG}/config.sh presence, and current value. If the value is empty, it'll prompt for the correct selection. If the user exits the selection, the installer alerts them that the choice is required, then exits the installer.

Later, after the make install completes, if the camera selection was required, the installer sets the camera value.

[EricClaeys]

Around line 48 could you add a comment that says something like config.sh not found yet because it hasn't been installed. It will be installed later in this script.

[linuxkidd]

@EricClaeys I've added a comment in that area now that explains things a bit. Let me know if you see anything else that needs tweaking.