fix: blog post links

[brianrclow]

Issue: In Advanced Concepts, section about Adding ObjectC/Swift Code(https://docs.nativescript.org/advanced-concepts.html#adding-objectivec-swift-code), the link to a blog post goes to a dead end. This is the link in the docs currently: https://www.nativescript.org/blog/adding-objective-c-code-to-a-nativescript-app

Solution: Update link to correct url: https://blog.nativescript.org/adding-objective-c-code-to-a-nativescript-app/. Also, I updated link in performance page (Step 2, right above summary: https://docs.nativescript.org/performance.html#benefits-from-using-lazy-loading )that had a similar incorrect blog url.

[rigor789]

Fixed our redirects, main issue was that www.nativescript wasn't redirected to nativescript.org without the www, but that should be good now.

[rigor789]

Including these anyways, to reduce the redirects - but landing on the old links should work fine now as well.