Remember acceptance for unsupported browsers.
Remember acceptance for unsupported browsers.

Addresses #3624.

This stores the flag in localStorage, after checking if localStorage is available. If localStorage is not available, the user will be prompted just like before this commit.

Signed-off-by: Travis Ralston <f36f6a6abc4b55589c96c71fceedf83e596b8f33@gmail.com>
vector-im/riot-web,vector-im/riot-web,vector-im/riot-web,vector-im/vector-web,martindale/vector,vector-im/vector-web,vector-im/riot-web,vector-im/riot-web,vector-im/vector-web,vector-im/vector-web,martindale/vector,vector-im/vector-web,vector-im/riot-web