Create a "Read Only" Mode for password entries

[hpoul]

Right now there is only one mode which is meant for reading and writing. Which can lead to a few usability problems.

e.g. #107 and related also #91

I think it makes sense to have a separate mode, so people don't have to worry about accidentally modifying an entry.
Another option would be to have the fields simply read-only disabled where clicks only 'copy' by default, but can be edited by pressing some button?

If anyone has ideas/feedback to the usability hear, add your comments!