Tidy Up: get_trigger_app()

[CharlieBatchelor]

As mentioned in #202:

get_trigger_app() Tidy Up

The configuration generation for trigger is quite messy, and should be tidied up. It essentially does two things:

1. For a given tp_config item passed to the function, it generates a list of Modules. For example, it does things like "For each link, create a TPChannelFilter module, TPBuffer module..." and so on.
2. It then connects up all the modules in the list according to what we expect/want the system to run like.

Each step is itself done in quite a convoluted order, and it would make it more readable to generate the configuration in a "top to bottom" sense, based on the trigger flow graph diagrams, at least IMO. Start with the channel filters, to TPSetTees, to heartbeats and buffers, and so on.