Stretch tab contents to available space also when there is extra space

When the tab contents were larger than the available space they were
limited to that space. Now, if the available space is larger than the
needed height the tab contents is also increased to fill it.

This ensures that the chat view will always stretch to the available
space, which in turn ensures that the "New message" input will be always
shown at the bottom of the sidebar like done in the main view (which was
not the case before when there were no messages or only a few).

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>

css/style.scss

@@ -970,24 +970,32 @@ video {
 	display: flex;
 	flex-direction: column;
 	overflow: hidden;
+
+	flex-grow: 1;
 }
 
 #app-sidebar .tabsContainer {
 	display: flex;
 	flex-direction: column;
 	overflow: hidden;
+
+	flex-grow: 1;
 }
 
 #app-sidebar .tab {
 	display: flex;
 	flex-direction: column;
 	overflow: hidden;
+
+	flex-grow: 1;
 }
 
 #app-sidebar #commentsTabView {
 	display: flex;
 	flex-direction: column;
 	overflow: hidden;
+
+	flex-grow: 1;
 }
 
 #app-sidebar .comments {