Mission improvements + FLF improvements

This one is a little more scattered than my last pull request, but basically it's about improving the missions in Naev. Notable changes:

- I repurposed the Empire Pirate Bounty mission into a generic bounty hunting mission, accessible by anyone. It is very easy to fail at (partly because of distractions from other pirates and partly from police stealing the kills), and bounty hunting jobs are not available in as high numbers as cargo missions, but the rewards are much higher (defeating a Pirate Kestrel awards about 1 million credits, while small pirate ships award about 300,000 credits).

- The cargo and cargo rush missions are no longer specific to any particular faction. This means you can get these missions at pirate bases and on the FLF base, in particular.

- The FLF base has all of the basic facilities: outfitter, shipyard, and mission computer. I felt that it was a pretty useless base if all it had was a bar. The outfitter and shipyard don't provide very many ships and outfits, however.

- The second FLF mission (pre02) has been rewritten. Instead of taking out three Dvaered patrols, you take out one. Also, you ostensibly do it alone, but are rescued by a group of FLF ships when unexpected Dvaered reinforcements arrive. This new pre02 doesn't require you to use any particular kind of ship, but it largely favors small ships; large ships, even very powerful ones like the Pirate Kestrel, have a rather hard time surviving the attack of the Dvaered reinforcements. If you have previously worked for the Dvaered, you are given an option to betray the FLF, in which case the FLF ships attack you.

- A new non-unique mission has been added for the FLF, based on the new pre02. It is the same, but the missions have varying fleet sizes, sometimes with a "boss" (a Vigilance or a Goddard), and harder ones have you working with a group of FLF ships which arrive late 5% of the time.

- Hidden jump points have been added for the FLF, providing shortcuts both to Dvaered space and to Frontier space. This makes travel for the FLF, and the location of the FLF base, much less impractical. All Dvaered systems with FLF presence are now no further than three jumps away from a planet that is not enemies with the FLF.

- The Empire is now listed as an enemy of the FLF, and vice-versa. It didn't make sense for the player to be enemies with the Empire because of befriending the FLF when the FLF weren't enemies with the Empire.

I also fixed a problem with autonav time resetting that caused it to fail with hostile ships not of an enemy faction (usually produced by mission or event scripts).