add basic class and interface to represent and listen model change events
make model listener have type argument
revert the previous commit
add a default event listener
add a new function to get source code from given DBVersion and DBSourceFile
add a function to get the offset of each element
add a helper class to get file contents
remove default listener
add model for source code view
add method to get start/end lines in the source code view model
add an interface to represent constants of UI
add a view for source code
add a controller for source code view
add a new event class to represent changes of segment pairs
add a function to recieve the change of segments in the code view
add view of segment pairs
remove SegmentPairView to reconstruct the structure of ui
add an event to represent segment change as well as its listener
add an event to represent segment change as well as its listener
add an event to represent fragment change as well as its listener