## Description:
More fixes flagged by pylint 2 that don't hurt to have before the actual pylint 2 upgrade (which I'll submit soon).
## Checklist:
- [ ] The code change is tested and works locally.
- [x] Local tests pass with `tox`. **Your PR cannot be merged unless tests pass**
* Add support for specifying custom headers for rest_command.
* Added headers configuration to behave similarly to the rest sensor.
* Replaced test_rest_command_content_type which only validated the
configuration with test_rest_command_headers which tests several
combinations of parameters that affect the request headers.
* exposed content_type in rest_command, which allows for manually specifying the content_type for more-strict api endpoints
* fixed up column length
Length was 86 chars, and it needed to be 79
* double import of HTTP_HEADER_CONTENT_TYPE
Removed the accidental double-import of HTTP_HEADER_CONTENT_TYPE
* moved rest_command-specific config value into component
* if no content_type, default to None
* unit test
* newline
* unused CONTENT_TYPE_TEXT_PLAIN
* removed the http-agnostic abstraction hass provided in favor of aiohttps hdrs constant
Ville Skyttä
James Marsh
Mike Megally
Paulus Schoutsen
Pascal Vizeli