Fix bug when editing config keys (#66)

[vzDevelopment]

There is a bug which means that when a config key is edited a new config is added but the old config isn't deleted (see #66).

I have implement the first (and easiest) option from https://github.com/fnproject/ui/issues/66#issuecomment-487006837 which makes the config keys readonly so that it forces the user to delete the old config line and add a new one rather than editing an existing config line which will cause issues.

To Test

Repeat the process described in the issue:

Create an app using the UI e.g.:

vzarola-Mac:testing vzarola$ fn inspect app ui-app
{
    "config": {
        "config_key_1": "value"
    },
    "created_at": "2019-04-26T12:06:29.825Z",
    "id": "01D9CRMC61NG8G00GZJ000000Z",
    "name": "ui-app",
    "updated_at": "2019-04-26T12:06:44.430Z"
}

Then click the edit app button and try to edit the config's key. The interface won't let you:

However, you can still delete that config and add a new config.

I've also tested:

• Creating an app with no configs set then editing it
• Adding new config values whilst editing an app
• Adding a config with the same key as one that is read only (it updates the config key to use the new value)
• Delete a config and add a new one at the same time
• Deleting all configs

Repeat the above this for function configs.

[carimura]

works as intended. awesome!

[carimura]

i'll leave it up to you to merge since you had an open note there.

[vzDevelopment]

Unfortunately I'm finding it hard to find time for the fnproject at the moment so haven't been able to get back to doing the refactoring I wanted. I think we should go ahead and merge - the code is following the current status quo and fixes a bug so think it's fine to do.