This adds a 'creative' privilege to survival servers which OPs can bestow
on admin or competent builders to give access to the creative inventory.

This fixes the missing item issue in creative inventory caused by using
1 instead of 0 for 'start_i'.

Dig time is modified according to difference (leveldiff) between tool
'maxlevel' and node 'level'. Digtime is divided by the larger of leveldiff
and 1. In creative mode, where the hand is redefined to have maxlevel 3,
this results in higher level nodes taking significantly longer to break.

Now, to speed up digging, hand 'maxlevel' and 'digtime' have been
increased such that nodes of differing levels have an insignificant
effect on digtime. Dig time for all nodes is now identical to that of, for
example, dirt nodes.

* Unused variables
* Unused values (assigned to variables, but overwritten before use)
* Defining already defined variables instead of reassigning to them.

Symbols used in search caused the game to hang with a grey screen,
for example searching for 'diamond;ingot'

Fix the glitch when players use the '-' character in their username
on a server, causing creative inventory to not pass page 2

This pull adds a new global variable called creative.formspec_add
that will allow mods to add to the creative inventory screen
without the need to fork the mod altogether.  Simple solution
that works already for inventory_plus' BACK button

Add the listring functionality https://github.com/minetest/minetest/commit/c977fbd9288d0e80019554411a2f1885f7760568