Improve the user experience for initial startup (resolves #697).

Sending this out early to get feedback. Things seem to work.

* Takes the server process into account when computing the 'mode-line'. If a given source file 'belongs' to a server process, but there is no connection present, the mode-line will read 'Starting...'. This motivated some refactoring of the 'owning-connection-for-source-file' logic, moving much code to ensime-config.

* Replenishes connection attempts if the server buffer shows any action.

* Pops the server buffer in a secondary window when you run M-x ensime (without stealing focus). The idea being to make it obvious what is taking so damn long.


The current code looks in `:source-jars-dir`  which is normally set to `.ensime_cache/dep-src/source-jars/`. This is where source jars are extracted so your new code should still include it.