libdeng2|Info: Improved Info parser

Line numbers stored in elements, configurable warnings for duplicate
blocks (so that special blocks can be disregarded).
Fixed|libdeng2|Record: Checking for existence shouldn't throw exception
libdeng2|ScriptedInfo: Added the "namespace" blocks

While parent blocks contribute their name to the final variable name
representing an element, the "namespace" blocks allow hooking up the
resultant variables into any record visible in the ScriptedInfo
namespace.

Also unlike parent blocks, "namespace" influences "inherits" in
addition to element identifiers and but does not prevent access to
the global namespace.
Client|Cleanup: Use "namespace" in fonts.dei