WebSession: fix version check on Your Account page

• Fix Invenio version check on Your Account page that was failing due to domain name move. Also, improve the version check WRT forthcoming `-rcN' numbering of release candidates. (closes #344)

• Note that the version check does not distinguish between stable and development releases; this may be improved later. Until then, use generic softer wording.

• Also, slightly amend the wording of other warning messages produced by various safety checks on the Your Account page when logged in as admin.