PLOT: fixed "file not read" warn. for empty files

Bug was caused when the respective data file was empty, thus no data was
added to the gnuplot scripts, and gnuplot threw a "file could not be
read" - warning
Fix: Empty data files will cause a zero-line to be added to the gnuplot
script.
PLOT: fixed "multiple wildcards"-warning

Bug: A warning should be thrown if there are 2 or more wildcards in one
mathematical expression of a custom plot. The former check also counted
wildcards used in the naming section of the expression, resulting in a
false warning.
Fix: Counts only wildcards in the actual expression section.
PLOT: fixed non showing functions

Bug: If a plot contained a mathematical expression with wildcard, every
functinon containing a '*' would be removed, due to a
wildcard-replacement attempt on said function.
Fix: Wildcard replacement skips functions as it should.
PLOT: fixed bug witth Type not add to customplots
PLOT: 2nd fix on "Type not added to custompl" bug

Bug: A PlotType set in a PlottingConfig would not have any effect on
custom plots. The previous fix didn't completely resolve the issue.
VIS: monitoring now starts immediately in live mode
VIS: fixed bug with dists/nvls not showing correct

Bug: If a metric had no values, it would cause the metrics distributions
and nodevaluelists to not appear in the dropdown menu of multi scalar
visualizers.
VIS: fixed runtimes not being added correctly

Bug: General Runtimedefinitions in a VisualizerConfig would result in
the runtimes being added to the legend, but not show up in the plot.
This was caused by a mismatching static string being used when adding
runtimes from general configs.
VIS: addition to previous fix + log output removed
VIS: added the field "orderId" for generalConfigs

All generalConfigs in VisualizerConfigs can now have an integer with the
key "orderId". GeneralConfigs will be processed according to their
orderId, starting at 0 and going up. If orderId is unset, the respective
values will be added last.
Note: Any rule with orderId of -1 will be added last. Any other negative
orderId will result in not added values.
PLOT: fixed gnuplot errors with candlestick plots
Bugfix for handling the DummyEdge
Updated Assortativity to match new metric types. Aggregated all nine
classes to only three. Use AssortativityU or AssortativityR for all
types of graphs (weighted, unweighted, directed, undirected) and set
details by parameters from now on.
Assortativity: replaced StringParameters in constructor and computation
methods by enums to prevent illegal values.