adds a separate weight implementation that can be used by nodes and edges
adds weighted edges and nodes using the new weight implementation
adds empty constructors to all weight implementations
adapts the updates to the changes in weights and changes the string representation

- the new weight implementation for nodes is adapted in node and edge
weight updates
- batch generators are adapted accordingly
- reader and writer are adapted accordingly

also, the string representation of updates is slightly changed
- node removal and node weight change:
  - the node is identified by the index only
- edge removal and edge weight change:
  - the edge is identified by index1 and index2 or the connected ndoes
removes all weighted nodes and edges (now obsolete)
First step of weight refactoring: generate them through GDS

Following: fixing red lights in metrics
WeightedGraph and NullWeight no longer needed - GDS transparently creates weighted elements if needed

This is directly put into the according test cases
Refactored outputting of Weights
Bugfix: assume a minimal initial size of 1
GeneratorsTest should use all edge and node types again
Reflect recent changes in the last test cases
Remove un-needed checks
Changed metrics to work with the new metrics structure
Make travis aware of a moved build.xml, and exclude one jar from build
Tiny bugfix for the test cases
Push some stuff from (Un)Directed to the upper class -- metrics might need additional changes, esp. in terms of checking for more duplicated code
New getter for edges by its attached nodes
Straight forward: remove old occurence of getting an edge by a dummy edge
Some fixes for the test cases
moves keywords for io from config to static fields