docs: add l10n term definitions from EFF glossary
docs: add l10n term definitions from EFF glossary

These are the terms that show in the source or journalist interface.

conorsch/securedrop,conorsch/securedrop,heartsucker/securedrop,garrettr/securedrop,ehartsuyker/securedrop,heartsucker/securedrop,micahflee/securedrop,ehartsuyker/securedrop,heartsucker/securedrop,ehartsuyker/securedrop,garrettr/securedrop,garrettr/securedrop,ehartsuyker/securedrop,conorsch/securedrop,conorsch/securedrop,micahflee/securedrop,ehartsuyker/securedrop,ehartsuyker/securedrop,conorsch/securedrop,heartsucker/securedrop,micahflee/securedrop,garrettr/securedrop,heartsucker/securedrop,micahflee/securedrop