Currently in `KMManager`, there's 3 methods to download a `KMKeyboard` (2 in `KMKeyboardDownloader`, 1 in `KMCustomKeyboardDownloader`) for the 3 use-cases respectively:
1. Add new keyboard (from the cloud)
2. Update a keyboard
3. Install a custom keyboard
This PR refactors the following:
1. Code from `MainActivity.checkUrl()`, `KMManager.KMKeyboardDownloader()`, and `KMManager.CustomKeyboardDownloader()` into a new activity `KMKeyboardDownloadActivity`.
Code for doing actual file downloads are kept in an `AsyncTask`.
2. `FileDownloader` moved to a separate util class.
3. Confirmation dialogs for downloading keyboards are also refactored into `ConfirmDialogFragment`.
At the moment, the keboard API isn't publishing the packageID, so using "cloud" as an in-term packageID.
As a result, keyboards get downloaded to /packages/cloud/
By design, kmp keyboards will unzip into /packages/packageID folders.
1. Moving default eurolatin2 keyboard assets
2. Move old keyboards to new packages structure
