Allow setting custom unlock strings

[mpldr]

My Lockscreen is basically mocking the BSOD and I would love to be able to show a "0 Characters entered" between the paragraphs.

Would it be possible to add an --unlock-string argument which accepts something like %d Characters entered?

[mindrunner]

Can you provide your config and png, etc for that one? :)

[mpldr]

png is in the issue, my current config is:

no-unlock-indicator

[mindrunner]

Would it be possible to add an --unlock-string argument which accepts something like %d Characters entered?

You could also convert the input to hex and show it as a Windows Error Code

[jirutka]

This was partially implemented in #52, but without %d.