Normalize some widgets appearance (those using ButtonTable)

This makes button heights similar in all uses of ButtonTable.
It depended on how the ButtonTable was used in each widget
(previously, first and last row may have different sizes than
the others).

buttontable.lua: more even buttons height whether zero_sep or not
framecontainer.lua: added padding_top/bottom/left/right (similar to
what was done for iconbutton)

The following widgets have been adapted for this, with some
additional fixes:

buttondialog.lua
buttondialogtitle.lua: wider title with adequate padding
confirmbox.lua + multiconfirmbox.lua: dismissable via tap outside
inputdialog.lua + multiinputdialog.lua: more even vertical padding between elements
imageviewer.lua
textviewer.lua
datewidget.lua
timewidget.lua

Additionaly: frontlightwidget.lua: fixed width of progress bar that
was exceeding window width since the Size scaling adjustements

frontend/apps/reader/modules/readerhighlight.lua

@@ -384,7 +384,7 @@ function ReaderHighlight:onHoldRelease()
                 },
                 {
                     {
-                        text = "_",
+                        text = "-",
                         enabled = false,
                     },
                     {