initial support for matplotlib toolwindow

Plots toolwindow is implemented as part of SciView toolwindow.
DataView merged into SciView.

Features:
- open toolwindow with plot on plot available (run/console/rebug)
- plots in toolwindow are in separate tabs with image editor inside
- tabs in toolwindow are closeable
- save plot as file action
- DnD to/from editor supported
- plots toolwindow could be disabled from Settings

python/helpers/pycharm_matplotlib_backend/sitecustomize.py

@@ -0,0 +1,23 @@
+import matplotlib
+matplotlib.use('module://backend_interagg')
+
+# We want to import users sitecustomize.py file if any
+import sys
+import os
+
+sitecustomize = "sitecustomize"
+parent_dir = os.path.abspath(os.path.join(__file__, os.pardir))
+if parent_dir in sys.path:
+    sys.path.remove(parent_dir)
+
+    if sitecustomize in sys.modules:
+        pycharm_sitecustomize_module = sys.modules.pop(sitecustomize)
+
+        try:
+            import sitecustomize
+        except ImportError:
+            # return our module if we failed to find any other sitecustomize
+            # to prevent KeyError importing 'site.py'
+            sys.modules[sitecustomize] = pycharm_sitecustomize_module
+
+    sys.path.append(parent_dir)