Timeout issues/improvements

**Is your feature request related to a problem? Please describe.**

I was just manually typing a password from KeePassDX onto a computer and it was taking a while as the site kept saying it was wrong (first due to me typing an O as a 0, but then because the site is clearly screwy) and because it's a long password. As I was doing this, it timed out on me multiple times, locking the database. It did this despite my periodically scrolling a bit and even after I increased the timeout (which was clearly not long enough, and also has security concerns associated with doing so. And then, when it would do this, every time I had to manually reselect the key file, sign back in, and search for and open the entry.

**Describe the solution you'd like**

There are multiple things that can be done to improve this:

1. Allow tapping and/or scrolling to reset the timeout (it looks like this was brought up as a possible problem is #562)
2. Add a warning that it's about to timeout, allowing the user to tap to keep it open (ideally with customizable warning time and vibration and sound).
3. Add a button to keep it unlocked until manually locked or the screen is turned off.
4. Add an option to remember the keyfile if locked due to timeout and/or if it's been under a user-defined amount if time since it last locked.
5. Have it (optionally?) remember the last open entry and automatically go back to it (this was also mentioned in #1185).

I'd ideally like all of these together, though I'd say 2, 4, and 5 are the ones I'd like the most and, if they're done, 1 and 3 aren't really necessary, and since 1 seems to have potential downsides noted in the other issue and 3 could be a security concern, with the others these two are not only not necessary but perhaps not a good idea.

**Describe alternatives you've considered**

Covered above.

**Additional context*
Add any other context or screenshots about the feature request here.

Start by reviewing the current timeout and database-lock behavior, then read the related discussions in issues #562 and #1185. The scope needs to be narrowed and the security implications agreed before implementation; done should define which timeout warnings, key-file or entry retention, and unlock options are supported.

Written by the indexing model from the issue text.