@naz.R
Well first thank you so much for publishing the code! 
Well you are free to choose a license that suit you, whether a proprietary license or a free and open-source license. (You can also decide not to put any license but then what we are allowed to do with your code and app can be a bit ambiguous, although normally standard copyright applies by default) . Be "the owner of the app" can mean several things, you would need to precise what you mean by that in order to define your license. For exemple most Free software licenses (Free software refers to freedom not price), will require to keep the copyright of the original author, and give credit. Owning the app in the open-store is also a different matter.
For me Free and Open-source software is fondamental to control individually and collectively the software we use, and guaranty that the software is doing what we want it to do, and not something the developer has added in its own interest to exploit users, their data, and their device ( That of course, I'm sure is not the case of your app at all
, but is unfortunately very common in the proprietary world ).
Basically everything in Ubuntu Touch system is Free and Open-source software, except binary blobs, given by the manufacturers, that are needed for the hardware, and it's kind of a trade-off to have to use them, because unfortunately in the mobile it's currently very hard to have acceptable hardware running without proprietary blobs drivers or firmware.
The Free software philosophy is personally the reason that I prefer Ubuntu Touch over Android. If it wasn't for that, I would use Android.