Resolve "OPAL-FEL (MITHRA integration)"

For #535 (closed)

• Move documenation from README to manual (will be done when MR gets merged)
• Move example to Wiki (will be done when MR gets merged)
• Remove unnecessary file and line info at the start of MITHRA
• Review use of *new
• Reorganise folders of MITHRA library lib , bin, ...
• Correct use of OPAL functions e.g. euclidean_norm()
• Remove unnecessary variables e.g. cfname
• OPAL constants instead of a "magic number"
• Remove unnecessary vector.clear()
• Move code from UndulatorRep.[cpp|h] to Undulator.[h|cpp]
• Remove ParticleMatterInteraction, , wakeField, BoundaryGemoetry
• File header with correct coding style
• Alphabetic order in CMakeLists.txt and other places in the code
• Conditional include MITHRA header files with #ifdef OPAL_FEL, ..., #endif
• Surround OPAL FEL code in other files with #ifdef OPAL_FEL, ..., #endif
• Check which header files are really required
• Use only C++ header files
• Check and correct indentation
• Use plural for variable names of containers (usually something we loop over)
• Bunch needs to be recovered by OPAL after undulator instead of using globalEOL_m = true
• Separate computeUndulator() in a file that is only compiled if OPAL_FEL enabled. EDIT 14-5: I think the idea is to put the computeUndulator() code in the Undulator class - Jochem
• Write unit tests for the new classes