src/: Update URL of GIMP User Group
src/: Fixes spelling error.
src/: Updated copyright information.
src/: Change Save to Export
src/: Keep file-export labels consistent with GIMP

File menu terms are moved from 'Export to/Export' to 'Export/Export As'
after the manner of 'Save/Save As'.

Bug: 719859

Content of this commit should be included with the followind commit
at once:
commit 3577007140a1f91436c44ae6107b47e72fedd931
Author: SimaMoto,RyōTa <liangtai.s16@gmail.com>
Date:   Sun Dec 22 18:43:52 2013 +0900