Feature/activate reservation

[LudwigSo]

The branch got a bit messy. Therefore the name is missleading and the PR contains the following features:

• UAVs use the reservation mechanismn from the charging stations
• The charge algorithmn has realistic values and is an implementation of the corresponding interface, which should simplify alterations or additions.
• The charging station is able to prioritize the efficient part of the charge algorithmn. As soon as an UAV reaches the second stage of the charging it will be exchanged with an UAV with lower current state when possible. This behaviour needs to be (de-)activated in the configuration.
• There are 4 statistical values recorded: usedPower, chargedPower (which differ by the efficiancy applied in the configuration and are technically rather one value), reservations and chargedMobileNodes.
• A new 3d model is added. While I am not totally happy with the appearance in the simulation I would definitly rate it an upgrade compared to our charging cow. ;)

Furthermore there were some bugfixes and code alterations applied.

The PR includes one known bug which is described here: https://github.com/ThomDietrich/multiUAV-simulation/issues/13

[ThomDietrich]

Hey! Thanks for the PR, just so you know, I'll look at and merge this PR on Wednesday.

Btw. how can anything be an upgrade to a charging cow? ;)