Added PlanOperation::getOperatorId()
Implement a simple copy interface for PlanOperations
Basing TableRangeView on const tables
Fix ctor of hashtable that excepts list of other tables
Adding task dependencies handles done dependencies

Before, adding a done observer to a task with the standard addDoneObserver()
method resulted in a dead lock if that task was already finished. Rather than
having a client check if a task is done before adding a dependency to it, this
is now encapsulated by the addDoneObserver() method.
Added Task successor/predecessor retrieval methods
Added Pipelining interfaces and examples
Performance data helper: Sorted operation durations
Merge pull request #316 from kaihowl/pullrequest/kh-pipelining

Pipelining + Necessary Changes
Change header of TPC-C tbl files to create a column store
Merge pull request #359 from Bensk1/tpccColumnStore

Change header of TPC-C tbl files to create a column store
Revert some unnecessary, buggy pipeline additions

This reverts commit 507d7bf02768676965781d8dabf4f2098a7c57f4.

Unnesting pointer calculators was very specific to the pipelining scenario
where chunks arrive as pointer calculators and the hash table needs to find the
lowest common structure to all chunks and then recalculate the positions based
on that. For general purposes in Hyrise, this will break. If the input to
a group by is a pointer calculator, this will not work; the group by assumes
pc-relative positions whereas the hash table would be based on absolute
positions.

Removed ineffective and buggy PipelineMergeHashTables.

The implementation basically rebuilt the piped hash table chunks from scratch.
To make it actually work without rendering the hash table useless for other
operators would have required more heavy lifting than seemed reasonable for the
gained benefit. Thus, it has been abolished.

Removed useless PipeliningHashBuild.
Merge pull request #361 from kaihowl/pullrequest/fix/hashtable

Revert some unnecessary, buggy pipeline additions
Delete .travis.yml

It's been sitting in time-out for long enough.