Minor bugs in instructions and prefs modal

[kliu57]

I discovered some bugs that arisen after the custom provider implementation

Bug 1 - Instructions page provider dropdown does not include the current provider when it is a custom-made provider

Steps to reproduce:

1. Create custom provider
2. Set custom provider to current provider
3. Clear the custom provider's api key
4. Close Prefs Modal, you should now see instructions page (if you don't scroll to bottom)

Expected Result: In instructions page, the dropdown should include and be currently set to the current provider which is the custom provider. And if you enter the correct api key and press Save button it should work.

Actual Result: The dropdown is not set to the current provider which is custom provider. And the Save button does not work since the password field is mapped to the custom provider but the provider dropdown won't show it.

Bug 2 - When switching to a provider with a saved key

1. Store valid keys in two of your providers
2. Set one of them as your current provider.
3. Clear the key
4. Close Prefs Modal and see Instructions page (if you don't scroll to bottom)
5. In Instructions page, use the dropdown to select the other provider that has a saved key

Expected Result: Just show the key but don't load the next page right away

Actual Result: Goes to the next page right away without validating the key

Bug 3 - Password field still focused after closing and reopening the Prefs Modal, validation issues

1. Clear the api key of current provider
2. Close the Prefs Modal
3. Reopen the Prefs Modal
4. Paste the correct api key

Expected Result: Validation should automatically occur and invalid key message should disappear. Also the field should not be focused when we reopen the modal.

Actual Result: Validation did not occur and invalid key message still there. Field is focused the moment we reopen the modal.

Bug 4 - We need to ban browsers from asking to save the key

This is important since in the prefs table we have many api key fields and if user use Chrome to save their key it won't get repopulated in the correct field. Also, we are storing the key in localStorage so there is no need for users to save their key to their browser.