add gitignore + ignore pycache dir for plugins

.gitignore

@@ -0,0 +1,7 @@
+# C extensions
+*.so
+
+# Pycharm
+.idea/
+
+tests/data/URHProject.xml

src/urh/plugins/PluginManager.py

@@ -35,6 +35,8 @@ class PluginManager(object):
         settings  = constants.SETTINGS
 
         for d in plugin_dirs:
+            if d == "__pycache__":
+                continue
             try:
                 class_module = self.load_plugin(d)
                 plugin = class_module()