Fix lingering crew in smaller ship

Fixes #2122

When buying a ship which holds fewer crew members then your current number employed, then deny purchase thereby giving the player the option of whom to dismiss from the crew to then match the maximum number of crew cabins, and try buying the ship again.

(Not sure I had to define the `ship:CrewNumber()` but couldn't see any other way to do it.)

I also noted that `HasCorrectCrew()` was not used anywhere, so I use it in Lobby now to check when requesting launch clearance.

Currently a small bug I'd like to understand: why do the messages come out like they do on the comms, half spliced in the middle? ping @robn (see screenshots)

I also disabled the "launch clearance denied" check from worldview since [no point in denying a permission that was never asked](http://pioneerspacesim.net/forum/viewtopic.php?f=3&t=194).


Also, when starting the game, I get a warning since I moved the `LAUNCH_PERMISSION_DENIED_BUSY` string from `core` to `ui-core`.

    core/en: token 'LAUNCH_PERMISSION_DENIED_BUSY' not foundb
    Initialized GL2 renderer

Not sure if this is just because the translation files are out of sync with the English one?

![ba3](https://cloud.githubusercontent.com/assets/619390/2604786/049be014-bb3e-11e3-8e9f-567e8d22afc8.png)
![ba1](https://cloud.githubusercontent.com/assets/619390/2604789/09dd0d28-bb3e-11e3-815d-5172cae3cfcd.png)