New server modal warnings

[jnugh]

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Summary
Fixes multiple warnings that were introduced by the new team modal PR.

Fixes #440

Test Cases
Check if I changed the '+' Button in the TabBar (I had to wrap it correctly and had to make some CSS changes).

[jasonblais]

Thanks @jnugh! Can you help submit it against the release-3.6 branch so we'll include it in the upcoming release?

[jnugh]

Changed the target and rebased the PR.

[jasonblais]

Thanks @jnugh for the quick fixes!

1. After refresh, one more JavaScript error remains, the other ones have cleared.

2. The style of the "+" icon is slightly changed with:

• overlapping the desktop tab bar divider line
• not being quite centered relative to the desktop server name

PS: I found a couple of other JavaScript errors when clicking around, not sure if these are related?

3. After clicking the "+" icon

4. When going to the Settings page

5. When clicking "Add new server" in Settings page

[jnugh]

1 und 4 have been there for some time already.
2 and 5 is easy to fix.

3. I have no idea right now - Didn't think of this. The button is now wrapped in a NavItem. Therefore a click on that button is forwarded to the tab listeners.
   This actually breaks multiple things a lot of things as we are not dealing with warnings but actual errors.

I have actually no idea how to wrap the button correctly in the navigation without breaking everything. @yuya-oc do you have an idea?

[yuya-oc]

1
This would be gone by removing initial nodeIntegration attribute from webview. It's unknown, so reported as warning by React. Existing tests would check whether node integration is correctly disabled.

3
TabBar.prop.onSelect() calls back the index of the selected item. For example, When "+" is clicked, it would call back "2" when there are two servers. But MainPage.handleSelect listener doesn't take care this.
As the result, the error message appears because MainPage.componentDidUpdate() tries to refer mattermostView2 which doesn't exist yet.

To fix this, I feel that adding onClickAdd prop to TabBar to stop using Button.onClick and handle Nav.onSelect to call back onAddServer is proper.

function handleSelect(key) {
  if (key === this.props.teams.length) {
    this.props.onAddServer();
  } else {
    this.props.onSelect(key);
  }
}

<Nav onSelect={handleSelect}>

Or using Button.onClick and:

function handleSelect(key) {
  if (key < this.props.teams.length) {
    this.props.onSelect(key);
  }
}

<Nav onSelect={handleSelect}>

4
It's shown because our components are not completely stateless. I think it's not easy to fix soon.

[jasonblais]

Thanks! I can create tickets for 1 and 4, no need to worry about those for this PR

[jasonblais]

@jnugh not sure if 3 is something you have time to work on?

[jnugh]

I simply added a key to the NavItem and do a check in the handler. Works fine for me :)
Very sorry for the delay to get the last commit in.

[yuya-oc]

Thanks for updating!

I feel it's wired that MainPage knows about internal key of TabBar. However it's an easy way for now.

After adding a server, the console shows an error. But it's not for this PR.

[jasonblais]

Looks good! Created a separate issue for the console error that shows after adding a server #468