Docs update for several classes

Namely: Dictionary, GraphEdit, Object, TileMap, Script, ScollBar,
ScrollContainer and SplitContainer

(cherry picked from commit 0dd526e062)

doc/classes/Dictionary.xml

@@ -20,6 +20,7 @@
 			<return type="Dictionary">
 			</return>
 			<description>
+				Creates a copy of the dictionary, and returns it.
 			</description>
 		</method>
 		<method name="empty">

doc/classes/GraphEdit.xml

@@ -228,6 +228,7 @@
 			<argument index="0" name="node" type="Object">
 			</argument>
 			<description>
+				Emitted when a GraphNode is selected.
 			</description>
 		</signal>
 		<signal name="popup_request">

doc/classes/Object.xml

@@ -398,6 +398,7 @@
 	<signals>
 		<signal name="script_changed">
 			<description>
+				Emitted whenever the script of the Object is changed.
 			</description>
 		</signal>
 	</signals>

doc/classes/Script.xml

@@ -24,6 +24,7 @@
 			<return type="Script">
 			</return>
 			<description>
+				Returns the script directly inherited by this script.
 			</description>
 		</method>
 		<method name="get_instance_base_type" qualifiers="const">

doc/classes/ScrollBar.xml

@@ -19,6 +19,7 @@
 	<signals>
 		<signal name="scrolling">
 			<description>
+				Emitted whenever the scrollbar is being scrolled.
 			</description>
 		</signal>
 	</signals>

doc/classes/ScrollContainer.xml

@@ -26,6 +26,18 @@
 			If [code]true[/code], enables vertical scrolling.
 		</member>
 	</members>
+	<signals>
+		<signal name="scroll_ended">
+			<description>
+				Emitted whenever scrolling stops.
+			</description>
+		</signal>
+		<signal name="scroll_started">
+			<description>
+				Emitted whenever scrolling is started.
+			</description>
+		</signal>
+	</signals>
 	<constants>
 	</constants>
 </class>

doc/classes/SplitContainer.xml

@@ -16,6 +16,7 @@
 		<member name="collapsed" type="bool" setter="set_collapsed" getter="is_collapsed">
 		</member>
 		<member name="dragger_visibility" type="int" setter="set_dragger_visibility" getter="get_dragger_visibility" enum="SplitContainer.DraggerVisibility">
+			Determines whether the dragger is visible.
 		</member>
 		<member name="split_offset" type="int" setter="set_split_offset" getter="get_split_offset">
 		</member>

doc/classes/TileMap.xml

@@ -171,6 +171,7 @@
 			<argument index="1" name="value" type="bool">
 			</argument>
 			<description>
+				Set any collision layer to be [code]true[/code] or [code]false[/code].
 			</description>
 		</method>
 		<method name="set_collision_mask_bit">
@@ -296,6 +297,7 @@
 			Tile origin at its center.
 		</constant>
 		<constant name="TILE_ORIGIN_BOTTOM_LEFT" value="2" enum="TileOrigin">
+			Tile origin at its bottom-left corner.
 		</constant>
 	</constants>
 </class>