Add application view for the messaging system

[jacoblxliu]

Both inbox and sent items will be displayed here by toggling the view. Inbox messages include

• The requests you receive as a team leader from potential team members
• The invitation you receive as a potential team member from team leaders
• Maybe other messages depending on the communication system is implemented on the backend. Sent items include
• The invitation you send as a team leader to a potential team member
• The request you send as a potential team member to team leaders
• Maybe other messages depending on the communication system is implemented on the backend.

[jacoblxliu]

basically finished after d20d0e8367ad5e37467c4587d18f377277188af8