refactor: move more of start fiddle flow to main process

[dsanders11]

Currently when a fiddle is started, the START_FIDDLE IPC event is sent from the renderer to the main process, with all the parameters needed to start the fiddle. This PR changes the flow to drop the parameters on START_FIDDLE and instead add a new GET_START_FIDDLE_OPTIONS IPC request from main -> renderer to get those parameters. This lets us decouple the starting of a fiddle and will let us isolate the run button.

This also lets us consolidate more of the run fiddle logic into the main process and simplifies the flow instead of having a split brain where the renderer was driving some of the process. As a result we can drop the CLEANUP_DIRECTORY and DELETE_USER_DATA IPC events.

[coveralls]

coverage: 88.64% (-0.02%) from 88.661% — build/refactor-start-fiddle-ipc into main