App settings and flags

[marcincichocki]

• [ ] parse cli flags in main process
• [x] merge default, json and flags and set it as initial state
• [x] feed it to worker and renderer

Flags that have to be changed in some way:

• --key-bind electron is using different format
• --lang (?) that would require i18n in react
• --skip-update-check(?)

Electron client settings:

• [ ] width/height set by user
• [ ] position(?)
• [x] selected monitor(shouldn't it be in flags?)
• [x] list of monitiors

[marcincichocki]

Saving width/height and position of main window is non essential feature, other settings and flag are implemented.