Refactor and fix Smartcard handling code

In preparation for OpenPGP card support

• The check / eventcounter code does not work as this code assumed

so the polling for that was useless. (Kleopatra only detected
smartcards on launch before this commit)

• We now soely rely on the filesystem watcher to get notfied about

smartcard changes. This is also what GPA does.

• Card is now a new class to manage the information we have about

a smartcard. This will be more information for OpenPGP smartcards.

• We are now prepared for more Card Types (like OpenPGP) and not

only for Netkey cards.

• No more boost required.
• Fixed Serial number detection. This never worked because SERIALNO

is a status and not data.