fix some bad indentation
define `$product_fields` as public var not static

also remove unused instance var `$order_fileds`
`$order_fields` is used and is a public var

reverts part of previous commit
set timezone in own method instead of on construct
bump version to 2.4
re-indent the file properly
fix spacing issue
coding standard adjustments for constant definitions
order saving: adjust for coding standards

spacing adjustments & proper sanitizing data
activation function adjustments

coding standard adjustments + add missing output escaping
rewrite `product_write_panel_tab()` function

use printf instead of open/closed php brackets. easier to read and fits better with coding standards
refactor product/software panel

code standards, security/escaping and legibility
minor fixes to product/software panel

some fixes for the previous commit:
* properly output the field classes
* properly output the checkbox
* fix the js used to control the upgrade fields
fix PHP notices in the updater class
update product meta saving code
admin field helper

add a helper function to build out fields that go into the metaboxes
adjust the order metabox to use the new helper + other small fixes to it
adjust the product metabox to use the new helper
update activation meta box code

minor clean up for code standards and escaping
update the product_save_data() function

code standards and minor readability cleanup
update the order_save_data() function

* proper data sanitization
* code standards
add missing closing bracket