Use latin1 encoding most of the time where default encoding was used
before. Qt 4 assumes latin1 by default while Qt 5 uses utf-8 which is
not what we want.
Use utf-8 encoding in some places where default encoding was used before.
This includes strings coming from RPC.
Fix an issue with SortMode::names[] (filters.cc) where missing comma
between "sort-by-queue" and "sort-by-ratio" resulted in two array entries
being merged into solid "sort-by-queuesort-by-ratio" string and all the
following items being shifted compared to their enum counterparts.
Among other things,
* fix turtle icons size (20x14 -> 16x16)
* use QIcon states instead of changing the turtle icon ourselves each
time (unchecked - off, checked - on)
* make speed limit action in tray menu checkable
* simplify status bar buttons drawing and use QToolButton instead of
QPushButton
Make squeeze labels (used for values on Information tab) display tooltip
on hover if their text doesn't fit. Make selective labels (same as in
GTK+ client) text selectable with keyboard in addition to mouse.
Prevent dialog width growth occured before to fit long error texts.
