TSP-4673 Remove ticketscript-specifc references and general cleanup

Lots of non-functional changes, most notably:
- added support for triggering build plans that don't have stages
- replaced Bamboo's shortKey variables with 'key', so the TSP- prefix was no longer needed
- de-duplicated Bamboo API call handlers into a single 'call' method
- fixed Bamboo client variable scoping
- tried to avoid callback hell as much as possible in Bamboo client
- completed template configuration file (config.js)