Notify sponsors whether venues have exhibition space or not

[iandunn]

When sponsors are sent automated e-mails about new WordCamps, they should be notified whether or not the venue has exhibition space.

To do this, we need to:

1. Add a checkbox to the WordCamp post type
2. Add a placeholder shortcode to Organizer Reminders plugin

[bansod_deven]

Added a Patch.

1. Added a 'Is Exhibition Space available ?' Checkbox to WordCamp Post Type in the Venue Section.

2. Placeholder Shortcode venue_has_exhibition_space? added in Organizers Reminders Plugin.

Needs Testing though I could not test if the mails are going as expected or not.

[bansod_deven]

Patch for #720 Meta

[iandunn]

In 1232:

WordCamp Post Type: Add a field to track if venues have exhibition space.

Props bansod_deven
See #720

[iandunn]

This looks good, thanks :)

I committed the first part in r1232. One small change I made was to use checked() instead of manually outputting the attribute.

I haven't committed the other part yet, because we now also want to tie the new shortcode to ​sponsorship packages, because only certain packages include exhibition space, so only those sponsors should have the information included in their email.

The packages are currently being updated, though, so we'll need to wait until they're settled in order to know what criteria we can use to programmatically determine whether or not to include the message about space being available. That may be done later today, though.

Once that's added, the second part just needs a final review/test and then it can be merged.

[iandunn]

Refresh after r1232

[iandunn]

In 5356:

WordCamp Organizer Reminders: Add the venue_exhibition_space_message shortcode

Props bansod_deven
Fixes #720