Improved chat view and message bar (#33)

* added style.css and style-dark.css

* keep message text view sensitive at all times

* improved chat view ui and message view

* added clamps for chat container and message

src/alpaca.gresource.xml

@@ -1,6 +1,8 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <gresources>
   <gresource prefix="/com/jeffser/Alpaca">
+    <file>style.css</file>
+    <file>style-dark.css</file>
     <file preprocess="xml-stripblanks">window.ui</file>
     <file preprocess="xml-stripblanks">gtk/help-overlay.ui</file>
   </gresource>