[538-kea-should-not-store-anything-in-var-kea-lsb-violation] Moved to localstatedir/lib/kea for state files

- Fixed one doxygen error in HttpListenerImpl
- Described lifecycle of the transaction within the Http connection.
- Use another variable in HttpConnection::doRead to be less confusing
- Fixed a typo in Http connection.

- added support for fedora 30
- improved creating system boxes
- fixed installing cassandra and postgres dependencies on fedora 30

Added ChangeLog entry

doc/Makefile.am
    Removed netconf BAD example configs

src/bin/keactrl/Makefile.am
    Only install kea-netconf.conf when sysrepo is enabled

src/share/yang/modules/Makefile.am
    Only install yang modules when sysrepo is enabled

[540-recommend-moving-hostname-char-set-and-hostname-char-replacement-out-of-dhcp-ddns] Added ChangeLog entry for hostname-char-* at global scope

[540-recommend-moving-hostname-char-set-and-hostname-char-replacement-out-of-dhcp-ddns] Final improvements

[540-recommend-moving-hostname-char-set-and-hostname-char-replacement-out-of-dhcp-ddns] Checkpoint between DHCPv6 regen

[540-recommend-moving-hostname-char-set-and-hostname-char-replacement-out-of-dhcp-ddns] Checkpoint before regen (2)

[540-recommend-moving-hostname-char-set-and-hostname-char-replacement-out-of-dhcp-ddns] Checkpoint before regen