Merge branch 'release-0.4.3' into dev
o feature54 : DownloadDemoDipydocs class : download and remove demonstration
              DipyDocs.
o feature53 : Splashscreen is now centered with the main window.
o feature52 : Fixed a bug in the way the UI updated the commentary zone : this
              zone can now be updated only if a specific flag (bool
              UI::selected_text_and_blocked_commentaries) is set to false. This
              flag is set to true if, in RMODE, a portion of text has been
              selected.
o feature51 : The PosInTextRanges class doesn't use an unordered_map anymore but
              a map, allowing to store sorted keys.
o feature50 : (MainWindow::add_open_menu) added a special display to
              "File>Open>" if no Dipydoc could be found.
improved messages on splashscreen and about message box
Merge branch 'feature55' into dev
Improved messages on splashscreen and 'about' message box.
added py_ui/ directory : draft for the UI
improved downloaddemo icons; added hidetoolbars, minus and plus icons
modified reading mode's icons : 128x64 -> 64x64
new UI with buttons in text zone
new UI with buttons in text zone : added qt/sourcetoolbar.*, qt/sourcezone.*
added new icon files : reading_[a|l|r]mode_[on|off].*
the commentary zone has now its toolbar
+/- buttons are now connected to the proper functions
maintoolbar.hidetoolbars button is ok
unique_toolbar > mainwintoolbar
hidetoolbars button has now two states : on/off
fixed a typo : 'adress' > 'address'
connect() -> QObject::connect() everywhere
improved messages in ~UI()
removed useless MainWindow::documentWasModified()
new compilation option : NO_STATUS_BAR
ordered compilation options in dipylonreader.pro