Automatically set UECIDE environment variable if unset

External third party scripts and makefiles can now access the UECIDE
environment variable to get the location of the "settings" directory.
This is the directory which contains preferences.txt and also usually
the compilers, boards, etc.  For instance, you could now use something
like:

$ $UECIDE/compilers/pic32-tools/bin/pic32-gcc ....

within a script.

This commit also standardizes the license boilerplate in all .java files
in the main UECIDE core source.