Messages buffer is intended to be of a fixed capacity (MAX_LOG_LINES),
which cannot be achieved by std::queue unless we manually pop() extra elements.
std::queue uses std::deque internally which most likely results in allocations performed continuously.
FixedSizeQueue keeps a single buffer during its entire lifetime, avoiding any allocations except the ones
performed by stored objects.
QTextEdit is heavy, similar in functionality to WordPad,
while QPlainTextEdit is lightweight like Notepad.
Qt documentation recommends using QPlainTextEdit for log viewers,
and it also allows to set automatic cutoff of oldest messages beyond a fixed point,
which we now set to MAX_LOG_LINES (5000)
