[Fixes #33] Replaced "www/" Cordova paths by Capacitor's "public/" ones

[Clovel]

What I did

• Replaced "www/" package paths by "public/". Cordova used to use "www/" paths whereas Capacitor uses "public/".
• Updated the README.md's instructions accordingly.

Bonus

• Updated the CONTRIBUTING.md instructions on what files to edit when contributing.
• Fixed unit tests by implementing a missing function in testUtils.ts.

What I tested

• CodePush + Capacitor + Ionic + React
• Tested on Android (for now. iOS test coming soon.)

[Clovel]

We should link this w/ issue #33.

[Clovel]

Setting this MR as WIP. Latest iOS test shows that my fixes aren't sufficient.

To be clear :

• This works on Android
• This does not work on iOS 14.5

[o-alexandrov]

closes #33 #21 it'll probably close #21 also, as it seems to have the same path-related issues