[Blur] Make blur more effective on scaled display

[jtheoof]

Following #17, the blur is not effective enough on scaled displays. Even smashing all the way to 500, the user has to do many passes to effectively blur sensitive texts on terminal or code editor.

Example trying to blur the following text on black background will lead to:

blur times (level 500) | secret password
----------------------------------------
0                      | passzero
1                      | passone
2                      | passtwo
5                      | passfive
10                     | passten

Ideas:

1. Transform the blur level into an input, where users can go crazy
2. Make it Low Medium High setting
3. Give it an insane value not configurable (if it's only used for sensitive data, which it probably is)