[svg2xml] fix destination path of generated files

[tbouffard]

Previous implementation was only designed to work on Windows OS

• the actual destination path was the concatenation of the provided destination path + the path of the parent of the source svg file. But it removed the first 2 letters from the parent source path (probably to manage the Windows drive)
• In addition, it put the whole path lower case, replace space by underscore, probably to work on old Windows versions that don't like space and mix cases when using the Command Prompt

On Linux (and probably all case-sensitive OS, so MacOS), this changed the destination folder a lot which made it very hard to find the generated file.

Changes done in this area in the upstream repo (commits ordered by date) and that have been integrated into develop on 2020-08-16

• 2020-06-22
  • "Changed stencil group naming mechanism to be more intuitive" jgraph@f0d2f73
• 2020-06-24
  • "Fixes group name generating and option for naming from config ": jgraph@b9058ba
  • "Less folders are generated at destination ": jgraph@1f232f5

There was still an issue because the path was still put into lower-case that has been fixed.
Several tests have been added to verify that the generation works on all OS.

[CLAassistant]

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