Add Image Entities for program images and channel icons

[shadow578]

This PR adds three new 'classes' of image entity for each channel:

• image.<channel>_icon: the icon of a channel
• image.<channel>_program_image_current: current program image
• image.<channel>_program_image_upcoming: upcoming program image

these entites can be enabled in the options flow. they are disabled by default.

additional changes:

• add additional mime type for gzip compressed responses
• for each channel, create a 'device' to group all entities belonging to this channel to

Images

Upcoming Program Image Entity	Channel Icon Entity

[codecov]

Codecov Report

Attention: Patch coverage is 95.23810% with 13 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
custom_components/xmltv_epg/image.py	88.78%	12 Missing ⚠️
custom_components/xmltv_epg/helper.py	92.85%	1 Missing ⚠️

Files with missing lines	Coverage Δ
custom_components/xmltv_epg/__init__.py	100.00% <ø> (ø)
custom_components/xmltv_epg/api.py	72.22% <100.00%> (ø)
custom_components/xmltv_epg/config_flow.py	97.56% <ø> (ø)
custom_components/xmltv_epg/const.py	100.00% <100.00%> (ø)
custom_components/xmltv_epg/coordinator.py	96.42% <100.00%> (+0.59%)	⬆️
custom_components/xmltv_epg/entity.py	100.00% <100.00%> (ø)
custom_components/xmltv_epg/model/channel.py	91.48% <100.00%> (+0.79%)	⬆️
custom_components/xmltv_epg/model/program.py	93.75% <100.00%> (+0.27%)	⬆️
custom_components/xmltv_epg/sensor.py	93.68% <100.00%> (+0.35%)	⬆️
test/const.py	100.00% <ø> (ø)
... and 8 more