improved dev lists view

Improved lists view by replacing class-based view to a more
flexible view suggested by tampakrap and mgorny.
add per-view caching on lists

Added a per-view caching to lists which reliefs server
from HTTP requests and improves performance.
Merge pull request #65 from mgorny/strong-auth-decorator

@strong_auth decorator
Merge pull request #63 from dastergon/improve_lists_view

Improved and added per-view caching on lists
Merge pull request #66 from mgorny/otp-ldap

Use LDAP as secret backend for OTP.
add url tag to templates

Using url tag the templates become more portable and respect the DRY
principle.
rename accounts_lists view to lists
Merge pull request #67 from dastergon/url_tag

add url tag to templates
Introduce get_bound_ldapuser() helper.