Rework privacyIDEA admin tool

[plettich]

The privacyIDEA admin client needs some updates / cleanups

• The tests only work partially, some need a running privacyIDEA server
• We should either require/install the yubico-package or disable the yubikey menu
• There is some code to be executed in the utils packages, we should remove it
• The audit sub-command is not working
• There is unused / untested / broken code
• Enable Python 3
• Catch SSL-Error and print some nice sentences
• Update build system