Fix #68: don't calculate list of fields sorted by tab order, just find the next/previous ones on the fly

Moved tab_index to Style (instead of Field), it makes more sense there, since it pertains to the layout of stuff on the card.
Added fancy mouseover effect to field borders. This might be slow, so I should add a setting to disable it.

TODO: document the changes

fix build on vs7.1 (older winapi version). EP_EDITBORDER_NOSCROLL doesn't exist there. We need a good way to test for it, or just upgrade to a new minimal winapi version

 * cannocial_name_form now outputs "_" where it used to use " "
   this simplifies some things, because now C++ names are also MSE internal names
 * added 'caption' property to fields. This is used instead of the name in NativeLookEditor, since the latter will now contain underscores.

Added ExportTemplate::byName
Use ExportTemplate::byName in main

fixed: write_image_file failed with --export with relative path, because the is-relative-to-target-dir check was wrong

Fix #67: remember the value of FilterCtrls when the control is destroyed, and set it again when the control is recreated

  condition ? wxString(something) : wxEmptyString
doesn't work, because wxEmptyString is a wxChar*, and g++ doesn't see the conversion.

TODO: move this function to another file

testset: ignore locale errors (except in a single testcase for them), otherwise all tests fail when there is an error in the locale

tests: consistent format for output, include some information on the machine running the tests, script for testing at top-level