Implement saving/loading of VizDB via creation/processing of CINT scripts.

TEveManager
-----------
1. Implement Load/SaveVizDB()
2. Add bool members controlling behaviour of VizDB during loading, in
particular whether to replace existing entries and update connected clients.

TEveElement
-----------
1. Implement top-level SaveVizParams() and virtual WriteVizParams()
that is called throughout the element class-hierarchy.
2. Add the following methods that can be called from the context menu:
   - void VizDB_Apply(const char* tag);
   - void VizDB_Reapply();
   - void VizDB_UpdateModel(Bool_t update=kTRUE);
   - void VizDB_Insert(const char* tag, Bool_t replace=kTRUE, Bool_t update=kTRUE);

Other
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Virtual WriteVizParams() implemented for the following classes:
TEvePointSet, TEveLine, TEveTrack, TEveTrackList and
TEveStraightLineSet.


git-svn-id: http://root.cern.ch/svn/root/trunk@24449 27541ba8-7e3a-0410-8455-c3a389f83636