Server side validation of RiveScript code

[kirsle]

The front-end enforces that RiveScript code must "compile" (not raise syntax errors) before being allowed to be shared with others, but the back-end doesn't do this. The back-end only makes sure that the source size is less than 64KB.

With the code refactor in rivescript-python#30 the server should be able to safely utilize the rivescript.parser module to parse the code to check for syntax errors while avoiding all the potential issues of accepting/processing arbitrary RiveScript code.