Gentoo ebuild for UrBackup

Changes:

• All upstream autoupdate code, files and UI elements have been removed, to avoid package management conflicts and any subsequent confusion
• gcc "warning: _FORTIFY_SOURCE redefined" corrected by first undefining then redefining
• Fixed bad perms on www files (executable bit is not necessary, and breaks both FHS and POSIX)
• Updated and Gentoo-fied "FILES" section of man page, and corrected formatting
• Installed compressed man page in FHS compliant directory
• Provided Gentoo-fied init script for OpenRC
• Removed redundant second copy of urbackupsrv binary from /usr/bin
• Use Gentoo-fied (and FHS compliant) ${localstatedir}, /var/lib rather than /var, for package database files
• Set owner and group to urbackup for ${localstatedir}/urbackup and ${datadir}/urbackup/www
• Honoured configure options for crypt, mail, fuse and zlib in USE flags