Make it easier for contributors to choose pictures for upload on the Commons Android app

1. At the bottom of the picker, there will be two buttons "Upload" to start the Upload Wizard with the selected pictures (replacing the already implemented ✔️ button currently available at the top-right) and "Mark as not for upload" to mark these pictures with a 🚫 overlay icon (and grey them out). For instance, family pictures are not meant to be uploaded to Commons. This state will be remembered even after restarting the app. Tapping "Not for upload" when all selected pictures are already marked as "Not for upload" has the opposite effect, a bit like pressing "Italic" twice in a text editor makes the selected text in Italic then normal. 2. Switch to hide/unhide pictures that are either marked as "Not for upload" or have been uploaded already. Hiding them allows the contributor to more easily spot pictures they might want to upload. 3. Currently, when selecting 3 pictures, they are numbered "1", "2", "3". Instead, please make all numbers always show the number of selected pictures, for instance, if 3 pictures are selected, they should all have the number "3", and be uploaded in the same order as their thumbnails are shown. 4. Add a fast scrollbar (ideally a Bubble scroll showing the date at which the pictures shown were taken). 5. UI when in full-screen mode -fullscreen starts when you long-press any picture in the custom picker 5.1. Show a small overlay indicating whether the picture is selected or not, showing the number of selected pictures. 5.2. Gestures: Left/right swipe to go from one picture to another. Swipe up to select the picture and show the next picture, skipping pictures that have either already been uploaded or ignored. Swipe down to immediately mark that picture as "Not for upload" and show the next picture.