Fixes #8414 - extracts validators from models

Also cleans up some unused validators looking for trailing whitespace
that is stripped by the StripWhitespaces concern.
Tried to make some sense from unmatching regexps and validation error
messages. Some validations might need a different regexp to check for what
they are actually supposed to validate - but atleast now messages fit
the actual validation.
fixes #8463 - remove i18n bundler group as it isn't optional

fast_gettext/gettext_i18n_rails are both runtime dependencies, not optional.
gettext_i18n_rails_js moved to assets as it provides no runtime functionality.
Fixes #5723 - Show host groups inherited via config groups in puppetclass index
fixes #8527 - pin rest-client to version compatible with current rbovirt

Pin rbovirt a bit in preparation for a jump in versions.
fixes #7487 - remove unused background-image containing UTF-8 character

UTF-8 was causing BOMs to appear in the precompiled CSS, which then prevented
these styles being applied, so bullet points appeared on the dashboard.
fixes #8467 - trends range selector is now visible
fixes #8459 - remove sp_subnet_id from api/hosts
Fixes #8428 - Connecting audits to existing users
fixes #8356 - refactor reset method for libvirt
Fixes #8499 - Link LICENSE from README
Fixes #8267 - accept template_url in call to foreman from proxy
Fixes #8421 - Host group search by OS attributes

Host group search by operating system only searches by name. Users
should be able to search by title and other fields, same as in the Hosts
index.
Fixes #8433 - Fix type transformation for all ENC-able NICs
templates - sync from community-templates