Delete a useless declaration of function and add comment for Client::getRoomIdByAliasJob.

Use new Client::getRoomIdByAliasJob instead of Client::getRoomIdByAlias.

Change GetRoomIdByAlias from Action to function that returns BaseJob.

Use boost.url for encode

Use helper function instead of useless properties

mxcUri, sha256, key, iv can be combined into one object.

FileHandler analyzes eventContent, checks whether it is encrypted and contains thumbnails, and performs download/cache.

Fix some incorrect variable name

Handle matrix link to a room alias.

Add GetRoomIdByAliasAction and Client::getRoomIdByAlias()

Use for instead of forEach.

Delete useless code.