Add precompiled headers to improve build speed

This adds a new first build stage "phase1" which consists
of precompiling `stdlib.hpp` in src/lib as a general header
that is then force -included into all .cpp compilations.

This severely reduces i/o seek times for the standard library
and large-ish parts of boost and should in turn drastically reduce
HYRISE compile time.
Merge pull request #97 from bastih/feature/precompiled_stdlib_header

Add precompiled headers to improve build speed
Improve performance of concatenation

When invoked with a large number of intermediate results, concatenation
was performing badly. This patch should fix such behavior.
Merge pull request #99 from bastih/feature/improve_concat_many_pcs

Improve performance of concatenation
Allow runtime extension of performance vector

It was not possible to extend plans at runtime,
thus we add the ability to add tasks at runtime
and expand the performance vector accordingly only
with pointers, ensuring that resizing the performance
vector won't result in moving memory around.

Merges #90
Merge remote-tracking branch 'upstream/master'
A bag of fixes for clang errors

Should fix a number of bugs in clang++
Improved makefiles, clang++ currently WIP
Enabled some more warning flags
Dialing back on the error messages

g++-4.7 does not particularly like -Wshadow for our code.
Add plugins to build system, move extra warnings to plugin
Fix clang++ virtual function call unhappiness
Merge pull request #105 from bastih/master

Fix clang++ behavior
Properly indent StaticRequestHandler
Improve handling of non-existing static files

Instead of SEGFAULT, we rather just send a nice error messaage.

Further, this abstracts out a few more parts into AbstractConnection,
so that a dynamic_cast isn't necessary any longer.
Merge pull request #107 from bastih/feature/improve_static_handler

Improve static handler to not segfault on non-existing files + some general improvements
Move taskscheduler tests into own binary
Merge pull request #108 from lordgeorg/taskscheduler-units

extract Taskscheduler units into separate binary
Fixing broken link in documentation
Updating the index doc