Add quasar's "row" class to ui.row

[falkoschindler]

This PR tries to solve #2881 by adding Quasar's "row" class to ui.row. Since it only adds

.column, .flex, .row {
    display: flex;
    flex-wrap: wrap;
}

we only need to deal with the new wrap setting. Therefore I changed

if wrap:
    self._classes.append('wrap')

to

if not wrap:
    self._style['flex-wrap'] = 'nowrap'

This way wrap=False counteracts "row"s flex-wrap setting.

For consistency I changed the wrap handling for ui.column from

if wrap:
    self._classes.append('wrap')

to

if wrap:
    self._style['flex-wrap'] = 'wrap'

But since there are no row-* classes in Quasar for layouting columns, there is no need to add the "column" class to ui.column.

I tested the new behavior with the following demo:

with ui.row(wrap=False).classes('w-40 h-40 border'):
    ui.label('A').classes('border col-6')
    ui.label('B').classes('border col-6')

with ui.row(wrap=True).classes('w-40 h-40 border'):
    ui.label('A').classes('border col-6')
    ui.label('B').classes('border col-6')

with ui.column(wrap=False).classes('w-40 h-40 border'):
    ui.label('A').classes('border h-24')
    ui.label('B').classes('border h-24')

with ui.column(wrap=True).classes('w-40 h-40 border'):
    ui.label('A').classes('border h-24')
    ui.label('B').classes('border h-24')