Implement ui.empty-message config option

Also removes some options that aren't going to be supported any time
soon.

config/aerc.conf

@@ -15,25 +15,12 @@ index-format=%4C %Z %D %-17.17n %s
 # Default: %F %l:%M %p (ISO 8501 + 12 hour time)
 timestamp-format=%F %l:%M %p
 
-#
-# The frames of animation to use in the UI for things that are still loading.
-# Seperate each frame with a comma.
-#
-# Default: "[..]  , [..] ,  [..], [..] " (note extra spaces)
-loading-frames=[..]  , [..] ,  [..], [..] 
-
 #
 # Width of the sidebar, including the border.
 #
 # Default: 20
 sidebar-width=20
 
-#
-# Height of the message preview, including the border.
-#
-# Default: 12
-preview-height=12
-
 #
 # Message to display when viewing an empty folder.
 #

config/config.go

@@ -17,7 +17,6 @@ type UIConfig struct {
 	IndexFormat       string   `ini:"index-format"`
 	TimestampFormat   string   `ini:"timestamp-format"`
 	ShowHeaders       []string `delim:","`
-	LoadingFrames     []string `delim:","`
 	RenderAccountTabs string   `ini:"render-account-tabs"`
 	SidebarWidth      int      `ini:"sidebar-width"`
 	PreviewHeight     int      `ini:"preview-height"`
@@ -171,9 +170,6 @@ func LoadConfig(root *string) (*AercConfig, error) {
 			ShowHeaders: []string{
 				"From", "To", "Cc", "Bcc", "Subject", "Date",
 			},
-			LoadingFrames: []string{
-				"[..]  ", " [..] ", "  [..]", " [..] ",
-			},
 			RenderAccountTabs: "auto",
 			SidebarWidth:      20,
 			PreviewHeight:     12,

widgets/msglist.go

@@ -89,7 +89,7 @@ func (ml *MessageList) Draw(ctx *ui.Context) {
 	}
 
 	if len(store.Uids) == 0 {
-		msg := "(no messages)"
+		msg := ml.conf.Ui.EmptyMessage
 		ctx.Printf((ctx.Width()/2)-(len(msg)/2), 0,
 			tcell.StyleDefault, "%s", msg)
 	}