vici: Add a command to reload strongswan.conf
swanctl: Add a --reload-settings command
swanctl: Add a --load-all command, performing --load-{creds,pools,conns}
swanctl: Fix description of load-pools command summary
swanctl: Complete --load-creds command summary
systemd: Provide a charon-systemd daemon targeting full systemd integration
plugin-loader: Support a reload() callback for static features
systemd: Add a native systemd journal logger
systemd: Discover and check systemd libraries with pkg-config during configure
systemd: Check if ./configure detected a systemd system unit directory
init: Provide a service file for charon-systemd using swanctl
init: Update starter systemd service to distinguish it from strongswan-swanctl
man: Skip installation of ipsec.conf/secrets manpages when not building starter
travis: Disable build of native systemd IKE daemon

Travis still uses Ubuntu 12.04, where no systemd libraries are available. Skip
systemd support on Travis until we have a more recent Ubuntu distribution.
Merge branch 'systemd'

Introduces a systemd specific charon-systemd IKE daemon based on libcharon.
Uses systemd APIs for startup control and journal logging and a new systemd
service unit using swanctl as configuration backend.