Handle file paths in a better way

[shape-warrior-t]

Currently, the files astra.db and logo.png are referred to in a way such that the specific files being referred to depends on the directory in which the code is run. For example, running astra/data/data_manager.py in the Python console creates an astra.db file under astra/data. It would probably be a good idea to change the code so that the file location being pointed to is independent of where and how the code for a module is executed -- although this might require some manipulation of paths.