* !WIP!
* Creates a new dialog widget for accepting keys - needed for keepassxreboot#838

For keepassxreboot#838, keepassxreboot#530

Basic implementation of allowing user to select which DBs to insert
KeepassHTTP Authentication Keys into.

For keepassxreboot#535

Disables the "OK" button when the key name edit is empty.
This avoids saving a KeepassHTTP key with empty key name, which causes
problems later.

TODO: Squash

To improve multi-db handling, we can move the checking for open
(unlocked) databases to the key accept dialog.

This means that even if the selected db is not open, the key can be
stored in another db as selected by the user.

This commit also adds a check for selected db's to the key accept dialog
so the dialog cannot be submitted if no db's to store the key are
selected.

Wrap strings presented to user in tr() for localization

Run clang-format and replace NULLs in all files touched by the PR