Support arbitrary QWidgets as browser tabs

[The-Compiler]

Just noticed there wasn't an open issue for this yet.

There should probably some Tab class which is the class of all tabs in the TabbedBrowser.

Then there could be a WebViewTab or so which is the glue between a QWebView and that tab "protocol" (in the Python sense of protocol), and there could also be some kind of WidgetTab or ScrollAreaTab or so.

This will also be useful for #666, then there can be a WebEngineViewTab.

qute:settings and others should then probably migrate to that instead of using a web page (cc @iggy)

[The-Compiler]

I spent some time finding out how to create a wrapper widget for QWebView so it's completely decoupled - this is what works:

from PyQt5.QtCore import QUrl
from PyQt5.QtWidgets import QApplication, QWidget, QLayout
from PyQt5.QtWebKitWidgets import QWebView

class WrapperLayout(QLayout):

    def __init__(self, widget, parent=None):
        super().__init__(parent)
        self._widget = widget

    def addItem(self, w):
        assert False

    def sizeHint(self):
        return self._widget.sizeHint()

    def itemAt(self, i):
        assert False

    def takeAt(self, i):
        assert False

    def setGeometry(self, r):
        self._widget.setGeometry(r)

class Wrapper(QWidget):

    def __init__(self, widget, parent=None):
        super().__init__(parent)
        self._layout = WrapperLayout(widget, self)
        self._widget = widget
        widget.setParent(self)

app = QApplication([])
wv = QWebView()
w = Wrapper(wv)
w.show()
w._widget.load(QUrl('http://cmpl.cc/'))

app.exec_()

Now the next question is what the API of this will look like, and what functionality the rest of the code needs.

[iggy]

Use cases I can think of: configuration/settings downloads (eventually) plugins view source (most other browsers have this, not sure it'd be a requirement though) developer tools informational (qute:version, etc) bookmarks release notes?

[The-Compiler]

Thanks for the useful list!

For display-only things (qute:version, release notes) I guess a webpage is preferable/easier.

:view-source already exists and uses pygments to generate HTML, so that should be fine as well.

[The-Compiler]

https://github.com/dhamaniasad/HeadlessBrowsers has some inspiration for APIs probably