Linking Request improvements

[Arrow768]

This can be improved

• Check if the byond key in the linking request has played on the server. If not output a error message
• Display the byond key the linking request has been filed for
• Add a page that allows users to see their past linking requests
• Add a page that allows admins to see all linking request (including cancelled ones)
• Ckey Sanitizing before writing them to the db

[skull132]

Ckeys ought to be sanitized when put into the SQL database, specifically into the ss13_player_linking table.

This would enable me to directly pull linking requests tied to a player by using the client.ckey variable. (By doing something like: SELECT blabla FROM ss13_player_linking WHERE ckey = :client.ckey;) Instead, in order to make the requests not care about user input error, I have to pull all requests that are open, and cycle through them with a while() loop, checking for if (ckey(query.item[1]) == client.ckey). Which is inefficient.