Allow overriding the location of exo plugins by setting and environment variable: EXO_PLUGIN_PATH

Can use : to separate multiple directories to search in.
Merge commit 'f85a1b84eeab444e46e5d5d4901958d8de010a04' into envPluginDir
Created a utilities class and put some useful class methods into it.

There is a lot of little things in the main exo.py that are useful to plugins.  So by putting them into a class, that class can be passed to the plugins.
Merge branch 'envPluginDir'
Use ExoUtilities
Stop if no data was read.
Tested start and end and fixed the differences for flush.