src: implemented move constructor/assignment for filepath

* improves indexing performance by roughly 5%
* switched to use uniqu_ptr for boost path to get rid of including boost in header
* added different methods to change the current FilePath or to make a copy and change that one
* used these methods appropriately throughout the code base
* removed exists() method from FileSystem because it is already contained in FilePath
* added const in some places

src/lib/data/storage/sqlite/SqliteStorage.cpp

@@ -4,7 +4,7 @@
 #include "utility/TimeStamp.h"
 
 SqliteStorage::SqliteStorage(const FilePath& dbFilePath)
-	: m_dbFilePath(dbFilePath.canonical())
+	: m_dbFilePath(dbFilePath.getCanonical())
 {
 	m_database.open(m_dbFilePath.str().c_str());