[GSoC] FileStorage:
Add base64 support for reading and writting XML\YML file.
The two new functions:
```
void cvWriteRawData_Base64(cv::FileStorage & fs, const void* _data, int
len, const char* dt);
void cvWriteMat_Base64(cv::FileStorage & fs, cv::String const & name,
cv::Mat const & mat);
```

Some CMake 3.x (2.8.12.2 is fine) provides broken build configurations
with following build error message:
    ld: fatal error: -soname: must take a non-empty argument

Linker command line sample contains this:
"-shared -Wl,-soname, -o"

combinations of translation, rotation, and uniform scaling equals four degrees of freedom

Correcting return type from videoDevice::findType to be int thus allowing detection of failed device init request

  * loosen the threshold only under aarch64
  * fix #6610

fix for #6598