Locate sqlite database in user-wide data location.

[magul]

Planning to have a system-wide installation process (at least for Windows), we should store database files in user-writable locations (not in the directory that application files are stored themselves).

ElectronJS provides here app.getPath function: https://www.electronjs.org/docs/all#appgetpathname, we should probably use app.getPath('userData') as a directory to store all user-centric data used in Alinka.