Speed up and clean up PrAddUTHitsTool

The tool that adds UT hits to long tracks (mainly used by the Forward Tracking and the Matching) is improved by avoiding memory (de)allocations and redundant accesses to the TES. The code is also cleaned up a bit. The tool gains a factor 2.5 in speed without changing the hit finding performance.

• replace some magic numbers with meaningful ones
• remove useless status code return

/cc @decianm @sstahl @peilian @chasse @lohenry