Botan 1.10 will be EOL'd this year. This patch is a rough port to botan 2 API. Also:
- Removes support for botan < 1.10 to simplify code (1.10 was released 7 years ago)
- Ports the cmake module to use pkgconfig, since botan-config doesn't exist anymore in v2.
- To minimize ifdef'd code, botan2 unique_ptr's are release'd
This only works with Qt5, since botan2 needs C++11. Not sure if there are any further qt4 releases planned (EDIT: fixed in latest revision)