Multi Input Files Support added

multiple -f options can be specified.
All file names will be added to a list and then opened.
Input Trees are searched in all input files. If trees with the same
name appear, the one from the last file is taken.
This allows to source data from different files. For example passing in MC
true information.

NOTE: The Directory Support has been removed. This can be solved with a shell script.
NOTE: Input file lines in config files: only one input file possible

NOTE: The first input file has a special role.
The Tags used for "IsAcqu" or "IsGoAT" are taken from this file.
Make sure to put your main data file first!

The pi0-example has been deactivated for now. Needs to be adapted in the same way as gaot_main.cc
Added Pluto MC true data Tree

cmake now finds pluto and builds goat with the GTreePluto enabeld.
Pluto can be disabled by running cmake with -DDISABLE_PLUTO=On

In the TreeManager I used #ifdef to enable/disable the include and creation of pluto stuff.
Not the nicest way, but works very well.

The GTreePluto is very simple and just copies the pluto data tree.
The output tree is named "data" for now, becasue pluto does it like this.