Fix context help for template data types

Summary:
This patch fixes broken code-context help for template data types. Old version has buggy behavior:

1) Place following code to some source file:

```
#include <cmath>
#include <math.h>
#include <vector>
#include <QList>

void test()
{
    QList<int> l;
    l.append(1);

    double x = std::sin(1);
    double y = sin(1);
    std::vector<int> v;
}
```

2) Place cursor to any function or templated type and call "Show Documentation" from context menu. Help page is NOT shown.

This behavior caused by wrong usage of documentation Url - we pass full qualified type (with template information like `QList<...>`), but documentation has topics only for plain data type like `QList`.

Test Plan: Tested on master branch with patched KDevelop plugings for Qt- and man- pages help.

Reviewers: kfunk, #kdevelop

Reviewed By: kfunk, #kdevelop

Subscribers: kfunk, kdevelop-devel

Differential Revision: https://phabricator.kde.org/D3205