Research Tree Improvements 3
Bugfixes. Fix bugs noticed by wz2100.net forum members.

1. Fixed doubling abilities of weapons in Unit designer in case of tanks with two weapons (reported by Ezio)
2. Unit design: "I do not know is this design researchable or not" -> "this might not be researchable for design" (reported by Ezio)
3. Fixed n keyboard_shortcuts.html "drop beacon: - F1+H, but infact its ALT+H (reported by Terminator)
4. Fixed typos noticed by richard14110
5. Added simple browser version check + warning (reported by Ezio)