Add image_medium_size variable in the templates
Add thead, tfoot in default default_good_tag_list
Test if file is already imported and close ic
Fix: output_hashtbl should now work for OCaml 4.00+
Moved css to an external file to benefit from caching.

Properties using variables still need to be in the .txt file, but this should be improved.
Do not support non-UTF-8 bases any longer

Got rid of the global reference utf_8_db and some dead code.
Cleanup: Removed gwc and renamed gwc2 to gwc

Reason: there is no need to create old-format database

TODO:
- allow importing several database like the old gwc used to
- check/fix according the changelog for version 6.03:
   !!! Beware !!! This functionnality is not completly functionnal when
    using gwc2. You can not edit twice the same place. If you want to
    edit more than one time one place, you have to do a consang between
    each modifications (because it will recalculate the indexs).
Cleanup: Removed ged2gwb and renamed ged2gwb2 to ged2gwb
Removed compatibility with databases created with version < 4.10
Removed compatibility with old patches