Expose the Member interface

[felldo]

Any help is appreciated and for open tasks see #1148

I can't test the whole PR so I think it would be better to merge this PR after the next release so people can try out the snapshot version long enough to test it. There are 100% things missing that still need to be adjusted due to that Javacord grow with the User interface.

Changes

• The own Bot member is now always cached regardless of what the usercache is set to
• Moved channel permission checks into their own interface if they are used for multiple channels (text, voice)
• Fixed UserChangeStatusEvent dispatching multiple times even though the status is the same (happened if the user shared multiple servers with the bot)
• Added Server#getMembersByRole

Breaking:

• Renamed Server#requestMember(long) to requestMemberById.
• Moved member specific methods from User and Server interface to Member.
• Removed Role#hasUser because a member object is required.
• Removed a lot of methods from the MessageAuthor as they are duplicated with the ones already in the member. For that an asMember method has been added.
• Renamed and moved some listeners and event for members
• Methods that returned an User object now return a Member if it's appropriate
• Removed permission check methods from the MessageAuthor interface

[RealYusufIsmail]

will have a look