swig-python: add support for python 2.7/legacy

In principle this is a big hack as it modifies the python class at
runtime. Since it's python legacy I hope it won't stay that long.

Note: Python 2 has no binary datatype so the API has changed a bit
Fixed the issue of lost formatting information
Fixed a number of memory leak bugs
Added a completion script for very basic bash completion
Fixed a clang compiler error #2
Moved commonly used functions to libelektra
adapt tests for yajl limitations

short time solution to make tests work
long term solution: Make plugin that rewrites directory
and parent key values to keys
some new todos + reformat to markdown
Merge branch 'master' of github.com:ElektraInitiative/libelektra
fix relation properties

to return false on null keys
add example for hierachy and iteration
Merge branch 'swig-merge' of https://github.com/manuelm/libelektra into manuelm-swig-merge
allow python-legacy to be used with swig 2.0.7
Merge pull request for python-legacy

https://github.com/ElektraInitiative/libelektra/pull/4

In principle this is a big hack as it modifies the python class at runtime. Since it's python legacy I hope it won't stay that long.

I was not able to let cmake compile both python + python-legacy in one step. I fear that's not possible at all as both modules use the FindPythonLibs cmake module which will only run once.

So the best way to force compilation of python-legacy is to run cmake with some extra defines. I think you'll need to define:

PYTHON_EXECUTABLE:FILEPATH=/usr/bin/python2.7
PYTHON_INCLUDE_DIR:PATH=/usr/include/python2.7
PYTHON_LIBRARY:FILEPATH=/usr/lib64/libpython2.7.so (or /usr/lib/libpython2.7.so)
fix memleak of test_backend
fix other memleak + document the issue

now no memleak again, 859 potential memleaks from dash, glibc or libxml
Fixed issues discussed in the pull request
small changes in top-level README.md
fix link
add documentation of CONTRACT

use README.md for plugins
first version of README.md filter (not in libAdd)
use "notification" as provider
avoid "filter" as provider
strange bug with metadata?