Improvements to termshark's dialogs

This change makes the Help dialogs and the new Columns dialog properly
modal. This has the effect of preventing the 'q' key from bringing up
the "quit termshark" dialog while either of these two dialog instances
are open. The former behavior causes a bug because termshark needs to
close the Columns dialog in order to trigger the termination of some
goroutines associated with the dialog's tshark filter validators, and
quitting via 'q' leaves the Columns dialog open. Termshark, by default,
will not terminate unless it has ensured all its goroutines have
stopped (to prevent leaks via behavior that is buggy but that I don't
necesarily detect otherwise).

go.mod

@@ -9,7 +9,7 @@ require (
 	github.com/blang/semver v3.5.1+incompatible
 	github.com/fsnotify/fsnotify v1.4.9 // indirect
 	github.com/gcla/deep v1.0.2
-	github.com/gcla/gowid v1.2.1-0.20210730201604-e21cc1dff36b
+	github.com/gcla/gowid v1.2.1-0.20210806031049-f60cd69d4bd7
 	github.com/gcla/tail v1.0.1-0.20190505190527-650e90873359
 	github.com/gdamore/tcell v1.3.1-0.20200115030318-bff4943f9a29
 	github.com/go-test/deep v1.0.2 // indirect

go.sum

@@ -59,6 +59,8 @@ github.com/gcla/deep v1.0.2 h1:qBOx6eepcOSRYnHJ+f2ih4hP4Vca1YnLtXxp73n5KWI=
 github.com/gcla/deep v1.0.2/go.mod h1:evE9pbpSGhItmFoBIk8hPOIC/keKTGYhFl6Le1Av+GE=
 github.com/gcla/gowid v1.2.1-0.20210730201604-e21cc1dff36b h1:mIGVx3Kq19ln5E25pwQtxCNmKi6rbrUhOgAtA1Vx+BE=
 github.com/gcla/gowid v1.2.1-0.20210730201604-e21cc1dff36b/go.mod h1:jQwZ6fAAnaylA+MkfgXLzjG0mTMStYixffw2jY0qG4k=
+github.com/gcla/gowid v1.2.1-0.20210806031049-f60cd69d4bd7 h1:4v2rkKvFsirRgM3C2UMPoxWxwM7Q9hlL/P31oB0YfIQ=
+github.com/gcla/gowid v1.2.1-0.20210806031049-f60cd69d4bd7/go.mod h1:jQwZ6fAAnaylA+MkfgXLzjG0mTMStYixffw2jY0qG4k=
 github.com/gcla/tail v1.0.1-0.20190505190527-650e90873359 h1:3xEhacR7pIJV8daurdBygptxhzTJeYFqJp1V6SDl+pE=
 github.com/gcla/tail v1.0.1-0.20190505190527-650e90873359/go.mod h1:Wn+pZpM98JHSOYkPDtmdvlqmc0OzQGHWOsHB2d28WtQ=
 github.com/gcla/tcell v1.1.2-0.20200927150251-decc2045f510 h1:TlEZ0DHOvn0P79nHtkfemw7XFn2h8Lacd6AZpXrPU/o=

ui/dialog.go

@@ -138,6 +138,7 @@ func OpenTemplatedDialog(container gowid.ISettableComposite, tmplName string, ap
 		dialog.Options{
 			Buttons:         dialog.CloseOnly,
 			NoShadow:        true,
+			Modal:           true,
 			BackgroundStyle: gowid.MakePaletteRef("dialog"),
 			BorderStyle:     gowid.MakePaletteRef("dialog"),
 			ButtonStyle:     gowid.MakePaletteRef("dialog-button"),

ui/psmlcols.go

@@ -325,7 +325,9 @@ func openEditColumns(app gowid.IApp) {
 		),
 		dialog.Options{
 			Buttons:         []dialog.Button{okButton, dialog.Cancel},
+			Modal:           true,
 			NoShadow:        true,
+			TabToButtons:    true,
 			BackgroundStyle: gowid.MakePaletteRef("dialog"),
 			BorderStyle:     gowid.MakePaletteRef("dialog"),
 			ButtonStyle:     gowid.MakePaletteRef("dialog-button"),