Adding loading indicator for syncing

When user updates a block, the update value will be send to server and
loading bar which indicates this process is popped up.
All js strings are from wp_localize_script

All strings used for scripts are now provided from wp_localize_script
Give product td a proper width and height

Table layout is quite unpredictable.
Fixing post-new newsletter experience

So there’s this issue: WordPress assigns ‘auto-draft’ status for newly
created ‘post’ (whathever the CPT is). Post with auto-draft status
cannot be previewed (wcng utilizes front end editing which requires
user to be able to access at least the preview screen of the post which
is available for post with draft status)

So this commit contains this workaround:

1. Hide the #newsletter-preview block if the status of the post loaded
is ‘auto-draft’
2. When user selects the template that will be used, send an AJAX call
to wcng_endpoint to modify the status of the post based on ID given,
then authorize the UI to fetch an iFrame which contains the preview
screen

I’m working on the endpoint after this commit
Adding change_auto_draft mechanism

Adding ajax processing for change_auto_draft to draft mechanism. Still
need tweak on template changing tho
change_auto_draft is now change_template

implication

- send the options selected on template regardless the post_status
- store the options selected on meta as _wcng_template
- start implementing changes on ajax handling structure