skin: load component positions from XML file

* removed horizontal layout (can be added later as skin)
forgot to add skin folder
skin image buttons
updated skin files
skin labels
skin meter's background
skin meter bars, overflow meter and maximum peak label
skin overflow meter and maximum peak label (continued)
skin stereo and phase correlation meter
updated build instructions
skin meter's background and meter labels
updated to JUCE 3.0.8

* fixes memory bug at shutdown of standalone plug-in
moved to FFTW 3.3.4
changed copyright date
updated legacy skin
updated default skin
renamed "meter_label" to "meter_graduation"
updated "about" and "validation" windows
dialog for changing the current skin
change file extension of XML skin files