This is a PR to introduce real TX management to HYRISE. It
 uses standard CID based optimistic concurrency control to keep track of
 modifications. Currently transactions are only guaranteed for inserts and
 concurrent inserts, but only if it's manually requested.

New Plan Operations:

  ValidatePositions - takes the current TID / lastCommited ID from the Query and removes all positions from the input table that are invalid for the current query
  Commits the current writes for the input table based on the current TID in the delta
  MergeStore - merges the input store using the merger that is specified in the class and thus uses the validity information of the instance

Other Changes:

  Removed SeqHeapMergerRow
  Rewrote SeqHeapMerger Dictionary Merge
  Merger will now remove invalid rows
  PrettyPrinter supports valid vector and cid for the store
  Cleanup for slice*() - The old slice*() methods were removed and renamed to partitionCount() and partitionWidth() to retain their original meaning. The semantics changed so that partitionWidth() will return the width in attributes instead of bytes. The actual width of the attribute has to be checked via th attribute vector itself.
  Store gets helper methods to validate positions and check and update commmit IDs
  Removing LogarithmicMergeStrategy
  Rewriting Merger and adding possibility to invalidate rows
  Removing old SeqHeapMergerRow
  Adding TX Context to Plan Operation
  Adding Commit Plan Operation, Tests for concurrent inseerts
  Moving TX Context and creating modification records for each table in the TX Manager
    per new TID a new Mod Record is created
    All modifying access to the mod record is protected by a spinlock
  Adding Performance regression for tx speed