Added dropping of packets

Dropping of packets was made possible in PDPModel. Tests for this
action were included in the PDPModelTests.
Added tests

Tests were forgotten in previous commit
Bug fix dropping + formatting change

Fixed bug in dropping packets: when action was continued, a delivery
action was put in queue instead of a dropaction.
Changed the formatting to only spaces and tab size 2.
Formatting

Second try to get the formatting right.
Override annotation were missing

Added override annotations who went missing.
Adding white space

Added some white space to conform with previous version.
Conform format

Effort to conform to format of previous versions.
Merge branch 'develop' of https://github.com/maartn/RinSim into develop
merge drop parcel method created by maarten
removed unused imports