Allow users to name backups when calling dumpdb

The default name doesn't always make sense for users, sometimes you want
to explicitly specify a name upfront. Add an optional argument to dumpdb
for this. Defaults back to old behavior.
Mendix 5 document exporter bugfix

this correctly replaces the proposed start-runtime.sh file, by actually setting
the classpath instead of dropping back to a .jar. Some cleanup was needed in
__init__ for config.py to set up the correct path, jar and or main class for
all cases (appcontainer version, run_from_source, <5 etc).
Mendix 5 document exporter lib fix

com.mendix.xml-apis-1.4.1.jar is found in runtime/lib and not in lib/
code style cleanup

 - rm comments, code should be clear
 - neu style pep8 allows lines to be longer than 79 if it enhances readability
 - move classpath setup to separate method
code cosmetics

if statements is clearer when using use_hybrid and checking whether
runtime_version is < 5 instead of 'not runtime_version >= 5'
Merge remote-tracking branch 'origin/dumpdb-naming' into develop
dumpdb usability

allow spaces in filenames. if anything is provided as an arg use it as a
filename, otherwise default back to old behavior