DebugCard: Support string item IDs

The /give command has, for a while, said things like:

Warning: Using numeric IDs will not be supported in the future.
 Please use names, such as 'minecraft:stone'

But setBlock() doesn't recognize those. It turns out to be pretty
easy to make it use string names when they are provided. Numeric
IDs are kept for compatibility, but the fallback for non-integers
is checkString() so that the diagnostic message will request a
string.
Added a bunch of checks to avoid fetching tile entities triggering chunk loads.
In particular, also added these checks in packet handlers. This may help with the robot issues. Hopefully. Maybe. Perhaps.
Merge branch 'seebs/setblock-names' of https://github.com/seebs/OpenComputers into master-MC1.7.10
Adjusted docstrings of debug.setBlock and setBlocks.