build: show configure summary using a pretty format

[rbuj]

sample output:

Configure summary:

    polkit-mate 1.26.0
    ==================

    prefix ...................: /usr
    libdir ...................: ${exec_prefix}/lib64
    libexecdir ...............: ${exec_prefix}/libexec
    bindir ...................: ${exec_prefix}/bin
    sbindir ..................: ${exec_prefix}/sbin
    datadir ..................: ${datarootdir}
    sysconfdir ...............: /etc
    localstatedir ............: /var

    compiler .................: gcc
    cflags ...................: 
    cppflags .................: 
    Warning flags ............: -Wall -Wmissing-prototypes

    Accountsservice ..........: yes
    Application indicator ....: yes
    Maintainer mode ..........: yes

Now type `make' to compile mate-polkit