External module required during `make` #434

Fixed by making Sympa::ListOpt not depending on Sympa::Language.

Refactoring and repairing login form

CSS cannot be updated if css.tt2 was older than previously generated CSS.

Create ${expldir}/${robot} directory if it does not exists

Template strings passed to javascript were not escaped

Fixed by escaping them with escape_cstr filter.

Timestamp of css.tt2 is not always increased by new installation.

Support for ARC signatures

Currently, estimated max. size of content is approx. 2000 octets, besides alt_emails attribute. Thus 2000 o is required and more is recommended.
- MySQL & SQLite: "text" type may still be used.
- ODBC: varchar allows 8000 o, sometimes 4000 o: Use "varchar(4000)".
- Oracle: Oracle 7 allows 2000 o and 8 and later allow 4000 o: Use "varchar2(2000)".
- PostgreSQL: Change "varchar()" to a compatible type "text".

- Cookie threw back by clients will no longer be used: Value of cookie will be kept in session store.

It is not obvious that this feature is really used. Maybe deprecated in the future.

- Won't keep track of "referer" by parameters in forms: Use session variable "redirect_url" instead.
- web_tt2/loginrequest.tt2 was deprecated: web_tt2/login.tt2 will be used.
- Several other fixups.

Refactoring help pages

Updating source texts according to fixes on en_US catalog

Formally drop support for Sybase