Pysignalclirestapi

* added support for `text_mode` parameter to Python API (thanks to braveheuel)

* replace `future.utils` with `six` package to support 'raise_from'

* added support for search endpoint - thanks to arjan-s (in https://github.com/bbernhard/pysignalclirestapi/pull/13)

* add methods to list, get and delete attachments by thielenf in https://github.com/bbernhard/pysignalclirestapi/pull/6
* Added verify ssl option by mietzen in https://github.com/bbernhard/pysignalclirestapi/pull/7
* Added support for missing send arguments by robin-thoni in https://github.com/bbernhard/pysignalclirestapi/pull/8

* added `requests` and `future` as external dependencies to `setup.py`

* added support for basic authentication (this allows to use the `signal-cli-rest-api` container behind a basic auth protected reverse proxy) - thanks to pico-prob