Issue title: Curiously recurring template pattern isn't indexed
 Issue body: Code as below isn't fully indexed :

// The Curiously Recurring Template Pattern (CRTP)
template <class T>
class Base
{
    // methods within Base can use template to access members of Derived
};
class Derived : public Base<Derived>
{
    // ...
};

Template class is indexed but all specializations are "non-indexed" so it is not possible to navigate to them.
 Comments: 
 Comment 0: Hm, I cannot reproduce this issue on Windows with Sourcetrail 2020.1.117. This is what it looks like for me:

![image](https://user-images.githubusercontent.com/16242920/81395028-365a6c80-9123-11ea-9825-3f879ef5d0fa.png)

{'source': 'GithubIssues', 'repo_name_with_owner': 'CoatiSoftware/Sourcetrail', 'issue_id': 612549699, 'repo_stars': 13600.0}