Reorg of proxies page with focus on anon proxies

[filippoweb3]

The points below must be fixed

• Rearrange subtitles: anon and time-delayed proxies are not proxy types
• Remove the part about how-to remove proxies, as already present in this support article
• This video seems to be outdated, I propose to add a new video tutorial
• Errors in anon proxies definition
• Reorganise the page to make it more clear and easy to follow

[nuke-web3]

FYI the name of anon proxies may change, most recently Pure Proxy was suggested: paritytech/substrate#7735

[DrW3RK]

Thanks Dan! @filippoweb3 Here is the PR on Substrate repo that tracks the renaming paritytech/substrate#12283

[filippoweb3]

@nukemandan @DrW3RK thank you, I added all relevant links about renaming anon proxies in the dedicated PR I am working on