list_channels return only with metadata (including the data produced
very big JSON saturating some client buffer implementation)
add get_channel_info to get full channel data with optional thumbnail
thumbnail is sent by default but can be avoided adding
"want_thumbnail":false to the JSON query
rename get_channel to get_channel_content
The code is not elegant as this version of the API will be soon obsolete
but it offer a bunch of channels functionalities, comments and votes
are not implemented yet
/channels/list_channels get all visibile channels
/channels/get_channel get content of a subscribed channel
/channels/toggle_subscribe subscribe/unsubscribe to a channel
/channels/toggle_auto_download set/unset auto-download for files attached
to posts in a channel
/channels/toggle_read mark a post as read
/channels/create_channel create a new channel
/channels/create_post create a new post in given channel, group_id
paramenter renamed to channel_id for consistence
mChannels use reference instead of pointer as it must be valid
for the whole lifetime of the object
RsGxsCommentService and derivatives use proper types for parameter, avoid
reference when unneeded