Sectorview tweaks

This PR adds a few improvements to the sector view which I did some time ago and have used for quite some time.

Because an image says more than a thousand words, let's use one:

![screenshot-20140111-192549](https://f.cloud.github.com/assets/1851410/1894563/88d76166-7af0-11e3-90b5-632be450ab68.png)

So the tweaks are:
- The sector coordinates of each system are printed
- It is possible to filter out the labels of uninhabited systems
- The detail boxes of hyperspace target and selected system are swapped. Why? Because, if you select a hyperspace target, lock it with ```SPACE```, select another system and then jump the selected system will automatically become the next hyperspace target. So, it's more logical, when they are displayed in this order (especially with the next addition).
- Not only display the distance, fuel requirement and duration from the current system, but also between hyperspace target and selected system (this is the line directly above ```Selected system``` in a bit different colour hue). This output assumes the same ship mass as now (i.e. it does not take the fuel consumption of the first jump into account).
- Not only draw a line between current and selected system, but also between current / hyperspace target and hyperspace target / selected system (so draw a triangle actually). This makes multi-hop trip planning a bit easier.