New types Account, Currency, Directory:
* New tagged uint types.
* Extract to_string functions from header to hide dependencies.
* Include what you use and C++11 for cleanups.
Move static treeNodeCache from SHAMap to the Application

These changes address two JIRA issues:

 - 291 unittest reported leaked objects
 - 292 SHAMap::treeNodeCache should be a dependency injection

The treeNodeCache was a static member of SHAMap.  It's now a
non-static member of the Application accessed through
getTreeNodeCache().  That addressed JIRA 291

The SHAMap constructors were adjusted so the treeNodeCache is
passed in to the constructor.  That addresses JIRA 292,  It required
that any code constructing a SHAMap needed to be edited to pass
the new parameter to the constructed SHAMap.

In the mean time, SHAMap was examined for dead/unused code and
interfaces that could be made private.  Dead and unused interfaces
were removed and methods that could be private were made private.
Update ripple-lib integration tests
Add ASIO strand to StatsDCollector
Finalize Autobridging implementation:
* Remove legacy OfferCreate transactor
* Misc. cleanups on LedgerEntrySet
* Fix a subtle bug with arithmetic operations on Quality
* Sanity check offers after taking