Refactor Ledger and support classes:

This performs a deep refactor on the Ledger class and its supporting
classes, in preparation for the move to shared_ptr<SLE const> in
places where the SLE is immutable and we are currently using
shared_ptr<SLE>.

Member functions are converted to free functions, the SLECache is an
explicit parameter, one line convenience functions are removed to
streamline the interface. Some callers are changed to use <SLE const>
instead of <SLE>

SLECache:
* Moved to its own header file

RippleState:
* Remove unused functions
* Store the SLE as const
* Simplify callers

AccountState:
* Remove unused members
* Simplify existing members

Ledger:
* Replace writeBack with insert and update
* Remove unused functions
* Remove LedgerStateParams
* Move getLastFullLedger to Application
* add entryCacheI, exists, fetch, erase
* Use boost::optional where it makes sense
* Make member functions free functions

Free functions:
* fetch: cache-aware SLE retrieval
* forEachItem, forEachItemAfter
* (various)

Builds/VisualStudio2013/RippleD.vcxproj

@@ -1480,6 +1480,8 @@
     </ClInclude>
     <ClInclude Include="..\..\src\ripple\app\ledger\PendingSaves.h">
     </ClInclude>
+    <ClInclude Include="..\..\src\ripple\app\ledger\SLECache.h">
+    </ClInclude>
     <ClCompile Include="..\..\src\ripple\app\ledger\tests\common_ledger.cpp">
       <ExcludedFromBuild Condition="'$(Configuration)|$(Platform)'=='debug|x64'">True</ExcludedFromBuild>
       <ExcludedFromBuild Condition="'$(Configuration)|$(Platform)'=='release|x64'">True</ExcludedFromBuild>

Builds/VisualStudio2013/RippleD.vcxproj.filters

@@ -2205,6 +2205,9 @@
     <ClInclude Include="..\..\src\ripple\app\ledger\PendingSaves.h">
       <Filter>ripple\app\ledger</Filter>
     </ClInclude>
+    <ClInclude Include="..\..\src\ripple\app\ledger\SLECache.h">
+      <Filter>ripple\app\ledger</Filter>
+    </ClInclude>
     <ClCompile Include="..\..\src\ripple\app\ledger\tests\common_ledger.cpp">
       <Filter>ripple\app\ledger\tests</Filter>
     </ClCompile>

Builds/VisualStudio2013/ripple.sln

@@ -3,7 +3,7 @@ Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio Express 2013 for Windows Desktop
 VisualStudioVersion = 12.0.31101.0
 MinimumVisualStudioVersion = 10.0.40219.1
-Project("{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}") = "RippleD", "RippleD.vcxproj", "{26B7D9AC-1A80-8EF8-6703-D061F1BECB75}"
+Project("{26B7D9AC-1A80-8EF8-6703-D061F1BECB75}") = "RippleD", "RippleD.vcxproj", "{26B7D9AC-1A80-8EF8-6703-D061F1BECB75}"
 EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution