Removed skills

This removes support for skills. The plan is to allow to implement the skills
as they were implemented before via attributes. This adds a lot more
flexibility to the server creators while also removing the confusion about
skills and attributes.

So this change does:
 - Remove the skillmanager with all its calls, the skill xml file, etc
 - Move exp giving to the script engine:
   + storing a list of all hits against a monster in c++
   + keeping track of beings which die or leave the map before they manage to
     kill the target (like before)
   + for now only the element can be used to check which attribute should
     get the exp.
   --> Allows to implement the old behaviour (and more) in the scripts
 - Remove the exp tag from the monster definition:
   + Since the server itself does not require it anymore it feels wrong to
     require it for EVERY monster. TODO: Add a system to add properties to the
     monsters/items.xml which allow defining things like the exp and allows to
     read the value from the script engine.
   + Small drawback, but it should not be hard to implement this property
     system.
 - Drop the level networking and calculation.
   + level calculation will happen via the attribute system later but i would
     prefer to do this in a seperate patch since this patch already got longer
     than expected especially since this requires to make setting correction
     points and available status points scriptable.
   + The level would be simply set as a attribute, the int number of it will be
     the level, the remaining digits will be the % number till the next levelup.
 - NOT remove any existing skill tables in the database update scripts.
   + There is no way to move them into the attribute table in a unified way
     (there are too many different way they could have been used). So server
     admins have to care about moving theirs skills to attributes themselves.
   + Keeping the old tables does not hurt for existing databases. So removing
     does not give any advantage/is required anyway. The now obsolote info
     about the EXP transaction is not removed for updated databases either.
     (The update script basically only bumps the version number without doing
     anything else.
 - bump the network protocol version --> old clients won't be able to connect.
 - bump the database version         --> serveradmins need to update their db.