WIP: add per-picture configuration capability to VTM (first version)

Add ConfigUpdateFile/-upd parameter to VTM, to provide a per-picture configuration file.

The configuration update file consists in a sequence of <poc> : <parameters> lines. Parameters are limited to those supported for per-picture update (currently a few PH/SH related parameters). See EncCfgUpdate structure in EncCfg.h and EncAppCfg::xGetUpdate() for the definition of the supported options, and EncLib::updateConfig() and EncGOP::xUpdateConfig() to see how changes are handled.

Example of config update file:

4    :  -qm 1 --SliceCuChromaQpOffsetEnabled=0
16   :  -qm 2 -qmid 1 -qmfile cfg/scaling_list/sample_scaling_list_file.txt
20   :  -qm 1 --SliceCuChromaQpOffsetEnabled=1
32   :  -qm 2 -qmfile cfg/scaling_list/sample_scaling_list_file.txt

POCs shall be provided in increasing order, but there can be some gaps. Note that config is read and stacked in display order, but updated in coding order, so gaps should not be understood as constant config in display order, but in coding order.

Software manual update is still missing; I would appreciate some guidance on how to document that feature.