If the API push URL is not set, present a prompt to configure the plugin rather than no metabox

[benlk]

Changes

If the plugin is enabled and no API push URL is set, rather than silently displaying no metabox, this changeset displays a prompt to the metabox-viewing user to configure the plugin.

The relevant settings page in the plugin is limited to users with the manage_options capability, so for users who don't have that capability, the following metabox is shown:

Users with the manage_options capability are given a link to the appropriate settings page:

The settings page is unchanged:

Why

For #51:

Just updated to the Wordpress API plugin version that was just released and I do not have a box anywhere for NPROne. I have looked in the documentation and that box is not available on my screen or options. What happened?

Questions:

• Does this affect tests? (This is @benlk's problem)
• Does the text in the meta box need to be revised?
• Are there any changes that need to be made to the settings page?
• Are there any parts of the plugin documentation outside of WordPress that need to be changed?

[benlk]

Regarding the question of whether documentation needs to be adjusted, readme.txt says this:

== Installation ==

1. Upload the plugin files to the /wp-content/plugins/plugin-name directory, or install the plugin through the WordPress plugins screen directly.
2. Activate the plugin through the 'Plugins' screen in WordPress
3. Use the Settings->NPR API screen to configure the plugin. Begin by entering your API Key, then add your Push URL and Org ID.

And the documentation at https://github.com/npr/nprapi-wordpress/blob/master/docs/installation.md also mentions configuring the API push URL.

I don't believe that we need to adjust the documentation.

[eteare]

Ben,
Meta box
For the folks who have manage_options capacity, can the copy simply read:
"The NPR API plugin's settings must be configured to push stories to the NPR API. Instructions here"
Configure the Plugin (big blue button)
Docs
I updated the docs to reflect changes we've made.
I don't think we need any more copy updates outside of the plugin.

[benlk]

manage_options meta box has been updated.