Dynamic Parallelization + Some Bug Fixes

This commit is an aggregate of work performed by JWUST and kaihowl mostly
consisting of the implementation of dynamic parallelization. Some bug fixes
are contained as well. The most important changes are as follows:

  * New radix join cost model by JWUST
  * Additive model for nested loop equi join
  * Use finalized types to eliminate virtual calls
  * Optimized PrefixSum
  * Optimized PrefixSumCalculation
  * Added a check for missing input table in tablescan
  * Changed StartTime of RequestParseTask to actual start time of operator
  *  Refactored / bugfixed / delta-enabled radix join
    - RadixJoin did not handle vertical as well as horizontal offset into
      containers correctly but mostly assumed too simplistic structures
    - Instead of just considering the main attribute vector, the join will
      now consider both attribute vectors and handles the delta correctly
    - Inputs to the join may need to be validated ("ValidatePositions") to
      provide a consistent view on inputs that are subject to concurrent
      modifications
    - RadixCluser and histogram showed a lot of code duplication. This has
      been refactored
  * added new op GetLastRecords
  * Store_FLV_F1_EQ_STRING_AND_F2_GT_INT expressions added
  * Eliminated shared_count contention in AbstractTable
Merge pull request #383 from kaihowl/feature/dynamic

Feature/dynamic