Exception handling, bug fixes, functionality

* Handle missing project configuration values
* Add support for mm_compile_rollback_on_error setting to allow project compile to not roll back when errors occur if needed.
* Support passing in Apex test classes to preselect them in the UI
* Lookup default python if it's not set
* Return build errors for display when rollback is turned off
* Update plugin settings handling to match sublime API
* Bug fixes for refreshing and indexing metadata
* Custom apex template support
* Delete metadata fix - was not using full path to metadata files when calling os.remove()
* Fix for missing json file - if a file is missing return empty dict instead of throwing exception.
* Add new template for a webservice ApexClass