Fixed some errors and issues; gave Apache group it's own name via property file.
Several changes:

        - all scripts now use the (externally exported, via 'export') environmental variable OE_INSTALL_SCRIPTS_DIR;
        - scripts are now moved to directories appropriate to them, e.g. modules/, dev/ etc.;
        - addition of mirth and java installer scripts
Refactored code to add user to groups.
Corrected and refactored variables.
Corrected variable names; added minor comments.
Added (empty) README files for each installation section.
Created new 'revert' target for turning mirth ML channels back to their .xml.in format (with appropriate regex substitutions).
Added all necessary sources. For the time being, the Mirth channels and Java sources (used by Mirth) will live in the conf/ directory but will ultimately make their way to their own projects. Apache configuration files included.