Seed phrase ease of use update

Make the following changes on seed phrase import:

- if space is pressed when there's only 1 seed word possibility, add the word to the input field and add a space
- if space is pressed when the character behind the cursor is a space don't update the input field (ie don't allow adding a lot of spaces between words).
- if space is pressed when there's more than one word possibility, or there are no word possibilities don't allow space to be added - if possible flash the word currently being written red for 250ms to indicate it's not a valid choice.

Note that copy/paste into the seed phrase input is something a user would almost never do - it is only for debugging. It should work though. Check it works correctly and fix if required.