Better vertical centering of text in its box

Decide baseline vertical position according to font metrics, instead
of the hardcoded 0.7 (in textwidget, which made the text a little
bit up in its box), and 0.75 (in toggleswitch, which made the text a
little bit down in its box). This usually gives a value around 0.72
or 0.73 with our ui fonts, which looks about right.
ReaderFooter: add bottom padding, now that our text goes a few pixels lower

frontend/apps/reader/modules/readerfooter.lua

@@ -116,6 +116,7 @@ local ReaderFooter = WidgetContainer:extend{
     height = Screen:scaleBySize(DMINIBAR_CONTAINER_HEIGHT),
     horizontal_margin = Screen:scaleBySize(10),
     text_left_margin = Screen:scaleBySize(10),
+    bottom_padding = Screen:scaleBySize(1),
     settings = {},
     -- added to expose them to unit tests
     textGeneratorMap = footerTextGeneratorMap,
@@ -186,6 +187,7 @@ function ReaderFooter:init()
         background = Blitbuffer.COLOR_WHITE,
         bordersize = 0,
         padding = 0,
+        padding_bottom = self.bottom_padding,
     }
     self.footer_container = BottomContainer:new{
         dimen = Geom:new{ w = 0, h = self.height*2 },