add some statements to get file changes
make version and source file be many-to-many
remove unnecessary index from data classes
add function to transform a collection of source files to map of them
add constants to represent each column name
add an abstract class to represent DAOs
add a function to refresh elements
add DAO for FileChange
add DAO for RawCloneClass
[MINOR_CHANGE] update test files
[REFACTORING] rename getDao to getNativeDao
add DAO for RawClonedFragment
[BUG_FIX] correct the class specified to get logger
create DAO for Revision
add a function to query with any prepared queries
add DAO for SourceFile and skelton DAO for Version which is required in the DAO for SourceFile
add DAO for VersionDao
add function to get DAOs in DBManager