rose app-run: builtin applications

This fixes #343, fixes #383, fixes #395.

In this change, I have re-branded `rose task-run`'s *task utilities* as `rose app-run`'s *built-in applications*. This makes it logical to introduce a `mode` setting in the `rose-app.conf` to specify a built-in application (as opposed to running a command).

`rose app-run`: I have introduced a `--app-mode=MODE` option to overwrite the `mode` setting. This would mainly be used internally by `rose task-run`. Users would normally use the `mode` setting to do this in the `rose-app.conf`.

`rose task-run`: I have removed both the `--no-auto-util` and `--util-key=KEY` options. The `--app-mode=MODE` option supersedes the functionalities of both of these options. `--no-auto-util` is achieved by doing `--app-mode=command`.

#395: The `rose_install` task utility is pointless, so it is removed.

#343: There was going to be a task utility for polling, this is now part of `rose app-run`. The main command (or built-in application) will not start until all the polling conditions are met. Functionalities are documented but should probably be extended.