Read only mode

fixed #144 

## Specification
- READ_ONLY mode is enabled when environment variable OACIS_READ_ONLY is set to '1'.
    - to boot OACIS with READ_ONLY mode, run `bundle exec rake daemon:start OACIS_READ_ONLY=1`.
- when READ_ONLY mode is enabled,
    - actions for creating, updating, and destroying records are disabled.
        - creating ParameterSetQuery, sorting simulators, and sorting hosts are exceptions.
    - links to these actions are also removed from views.
    - worker processes are not launched.