fix key events in FF66

[GWuk]

• fix change in behavior of key events in Firefox 66 (key "q" was disabled in all input fields)
• limit EventListener in SPH_PasswordProtector to password field

[GWuk]

fixes #10, #12, #13 and #14

[riedel]

would you mind building a release inside your fork. Repo seems to be dead :(

[GWuk]

You might want to consider PwdHash2 , which is available at https://addons.mozilla.org/en-US/firefox/addon/pwdhash2/ or https://github.com/GWuk/PwdHash2