Very minor code cleaning

Because this bug could create bad values in footprint libraries, this parameter is now checked
when reading a footprint description in legacy format

Pcbnew: fix Pcbnew name capitalization in messages.
About dialog: add a link to kicad-pcb.org

3D viewer: fix incorrect scaling factor when using nanometers.
Very minor other fixes

Fix some comments.  Enhance LEGACY_PLUGIN such that it can tolerate, then fix bad legacy footprint libraries containing duplicate footprint names.
This may have been an undocumented bug from more than a year ago, which manifested itself in *.mod files containing duplicate names.
LEGACY_PLUGIN loads those now quietly, but appends "_v2", "_v3", etc. to each succeeding duplicate sharing the same name.

base on expected text and current window font.

Expand the virtual world to 2.14 meters in the nanometer build of PCBNEW.
This seems to be holding up for now.

Eeschema (also Libedit and Libview) now starts always to the default grid (50 mils)
Gerbview starts with the last selected grid, but the validity is tested.
In Pcbnew the grid value is always displayed, so it should always be good.

Eeschema (also Libedit and Libview) starts always to the default grid (50 mils)
Gerbview starts with the last selected grid, but the validity is tested.
In Pcbnew the grid value is always displayed, so it should always be good.

Delete LEGACY_PLUGIN cache after deleting library of same name.
Remove automatically generted freerouter help header.
Add Normalize() to BOX2.
Clamp some values in the virtual space of drawframe.cpp

Should allow Pcbnew code easier to change and Gerbview code more understandable and easier to maintain.
Code cleaning (remove dead code, add comments).
Minor other enhancements.

Should allow Pcbnew code easier to change and Gerbview code more understandable and easier to maintain.
Code cleaning (remove dead code, add comments).
Minor other enhancements.

Fix some warning compil issues.
Add zlib sources to avoid build issues under Windows (zlib not installed with mingw).