Refactoring file layout

Moved files and folders around in an attempt to make usage more
user-friendly.
Refactors main script

Put everything into functions, hopefully making it easier to understand
and maintain.
Renamed main script

Decided 'bt-restore' was a better name than 'bt-image'.
Oops. Directory structure was wrong.

I had scripts inside the disk image master's folder.  Fixed.
Fixed bash functions.

Messed up the function declarations in bash.  Fixed.