[FEAT] Allow choice of symbols in generated passwords

[tarminu]

The password generation dialog allows one to select the character class(es) to be used for the generated password, but the options are not sufficiently granular.

Many websites require symbols from a restricted set, eg. [@#$=]. Currently one must manually edit the generated password to substitute the requisite symbols somewhere in the KP4A-generated string.

Please consider adding an option to specify additional symbols to be used in the generated password, as modified by the other options (especially the "At least one from each group" option).

Bonus suggestion: allow storing the password generation settings for an entry as a custom string added to the entry, so future password changes have the desired length, symbol mix, etc.