Add auto-enrollment for user without any token

[qlux]

Implements #20

[pep8speaks]

Hello @qlux! Thanks for opening this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file privacyidea_pam.py:

Line 115:80: E501 line too long (93 > 79 characters)
Line 127:80: E501 line too long (104 > 79 characters)
Line 133:19: E128 continuation line under-indented for visual indent
Line 239:33: E128 continuation line under-indented for visual indent
Line 240:45: E225 missing whitespace around operator
Line 241:80: E501 line too long (134 > 79 characters)
Line 250:80: E501 line too long (93 > 79 characters)
Line 257:80: E501 line too long (88 > 79 characters)