fixes #435

Suggested-by:

Clang-Tidy: The 'empty' method should be used to check for emptiness instead of 'size'

Suggested-by:

Clang-Tidy: Use auto when initializing with new to avoid duplicating the type name

This could actually change the behaviour here (could, because I don't
know if we can hit this special case) but this should hopefully the
correct way of doing this.

There's some detailed explanation of the difference here:
https://doc.qt.io/qt-5/qstring.html#arg-14

> This is the same as str.arg(a1).arg(a2), except that the strings
> a1 and a2 are replaced in one pass. This can make a difference if
> a1 contains e.g. %1:

```
QString str;
str = "%1 %2";

str.arg("%1f", "Hello");        // returns "%1f Hello"
str.arg("%1f").arg("Hello");    // returns "Hellof %2"
```

Suggested-by:

Clazy: Use multi-arg instead

Suggested-by:

Clang-Tidy: 'find' called with a string literal consisting of a
single character; consider using the more effective overload
accepting a character

All suggested by:

Clang-Tidy: The parameter 'X' is copied for each invocation
but only used as a const reference; consider making it a const reference

Suggested by:

Clazy: Use the static QFileInfo::exists() instead. It's documented to be faster.

Either by accepting an invite or manually using /converttodm and revert
with /converttoroom.

fixes #751

This ports the leave room dialog to QML, everywhere. There are now no differences between the various leave dialogs.

Fixes for pasting images, especially under windows where the image mime type detection doesn't work as expected

- Fixes scrolling to an event not being reliable
- Adds new /goto command that can open URLs, go to events, or go to message indexes.
- Refactored ChatPage::handleMatrixUri() to contain the handling originally in Nheko::openLink(), and makes it return a boolean based on whether the URL was handled internally or not.

see: https://github.com/vector-im/element-ios/issues/2353