Added the GUI of the spectators' tools.
Implemented the spectators' tools.
Added the state of the effects in the lore, in the spectators' tools' GUI.
Rewritten the TP inventory to allow more than 27 spectators.

Side effect: the size of the inventory matches the number of spectators.
Fixed NPE when a sectator clicks on an empty slot.
The fly speed is now changed, according to the requested speed.
The potions effects are restored when the spectator mode is disabled.

Also:
 - the "tools" effects are removed when the spectator mode is disabled;
 - the flying speed is restored.
The gamemode of the player is restored when the spectator mode is disabled.
Updated the API (spectators' tools).
Bugfix: the "Active" badge was only displayed with a speed effect.

(On the Spectators' tools GUI.)

Oops.
Removed "underwater vision", now in the night vision.

Because the underwater vision is not really effective without the night vision.
The night vision tool enables/disables both night vision and water breathing effects.

I use an eye of ender as an enable button, and an ender pearl as a disable button.
Merge pull request #16 from AmauryCarrade/spec-options

Spectators' tools, misc fixes, misc improvements
Finish "Spectators block players from placing blocks" problem.
Merge remote-tracking branch 'origin/master'
Remove potion effects when players enable spectate (they are already
added back afterwards)
Switch setAllowFlight and setGamemode so that creative mode over-rides
setAllowFlight(false)
Recognise all @AmauryCarrade's hard work! :)
Use constants as inventory titles for easy access & standards
- fixes broken player state viewer
Update to access plugin prefix "in a static way"
Fixed two integers being concatenated instead of added together.