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/SqliteIndexStorage.cpp

@@ -8,7 +8,7 @@
 const size_t SqliteIndexStorage::s_storageVersion = 15;
 
 SqliteIndexStorage::SqliteIndexStorage(const FilePath& dbFilePath)
-	: SqliteStorage(dbFilePath.canonical())
+	: SqliteStorage(dbFilePath.getCanonical())
 {
 }