Implement Backup/Copy Videos command in main menu and share phase

[Robin-rempel]

The local language user needs an easy way to copy local language produced videos to another drive or device, for either backup or sharing.

To do: In the main menu of the app, add a "Backup/Copy Videos" command.
In the share phase, add a "Backup/Copy Videos" button.

Tapping either of these should bring up a dialog box with these contents:

Backup/Copy Videos

Video types: [ ] mp4 videos [ ] 3gp videos Destination folder: [Browse] [path text box]

[Copy now] [Cancel] (status info)

Requirements:

• For the CopyNow button to be enabled 1) one or both of mp4 and 3gp checkboxes must be ticked, and 2) a destination path must be specified.
• The Copy operation uses those inputs, of course. The source folder is SPapp's current videos folder.
• Files that are not mp4 or 3gp should be ignored, not copied.
• The Copy operation happens on only videos that are new or newer files compared to the contents of the destination folder.
• A newer file overwrites an older file by this safer process (in case the copying is interrupted): 1) the old file is renamed by adding ".old". 2) The newer file is copied. 3) the .old file is deleted.
• SPapp remembers the selections and path used in this dialog, and presents these as the default next time.
• While copying, the status line is updated with the file name being copied, e.g. "Copying 001Story.mp4"
• When copying is complete, this dialog disappears. In it's place, a message box appears that says "Copying complete". The message box disappears with the next tap anywhere.
• If an error occurs while copying, the status line shows something like "error occurred while copying 001Story.mp4" and the CopyNow button is re-enabled.

Issue #216 is an alternative idea to this one.

[bryanwussow]

@johnml1135 Is it feasible for a Backup function in the app to copy all videos to an OTG device? (to a USB drive or SD adapter, for example)

[bryanwussow]

Bryan: #216 is an alternative design I think, that lists individual videos, so it would be more complex. #307 could be the first step towards #216. Robin: Bryan, the way you fleshed out #307 looks good to me. If that works, I think that should be sufficient and we don't need to do #216. I think #216 is redundant and be closed.