Add ScriptFileType rather than hard-coding "*.py"
Add CLASSPATH to environment
Simple invocation of something other than `python`
Migrate to named parameters for and_mimetype
Fix minor bug in script demo command
Remove double import
Add JYTHON_HOME to proc env and tidy up

For non-standard installs of jython, @manics has pointed
out that JYTHON_HOME needs to be propagated to the script
environment. If this is intended to be extensible, then
likely it will be necessary to let third-parties add to the
list of copied variables.
Fix doc typo found by @manics
Merge pull request #1324 from joshmoore/jy-scripts

Jython scripts (See #918)