Revert "send all create requests using a POST request (untested, could break, ymmv etc...)"

This reverts commit 8652491295afe804668aa11bb2d9d93b4ebfece1.
fixing specs for changed put -> post
allowing parent to be nil for some Records (for testing purposes only).
switching fake application to nil in test
Send the default headers in OAuth as well
Add new timezone field to organisation record

Xero added a timezone field to the organisation object, recently.
Add primary key to TaxRate to fix saving

We were having trouble saving `TaxRate` objects because the primary key was missing. This worked like a charm in our monkey patch.
Added archive status to contacts
Merge pull request #153 from warrenchaudhry/add_archive_status_to_contacts

Add Archive Status to Contacts
Merge pull request #150 from clodeindustrie/patch-1

Add Timezone Field to Organisation
change ARCHIVE status to ARCHIVED
Merge pull request #154 from warrenchaudhry/add_archive_status_to_contacts

Change ARCHIVE Status to ARCHIVED
add include_archived params for contacts
Merge pull request #155 from warrenchaudhry/add-include-archived-params

Add include_archived Params for Contacts
Add datetime_utc type to http_proxy

This allows fields of type datetime_utc to be used in where clauses.
The datetime_utc type was added in commit
cdae18e1694e3ce6aa9d333f3443f6d4591ad283 but was never added to
base_model_http_proxy, so you get empty where conditions when you
try to filter on fields of that type. This commit fixes that.
Merge pull request #157 from FiguredOnFarm/add-datetime-utc-field-type

Add datetime_utc Type to http_proxy
Fixes creation of TaxRates

Before, there was no primary key defined for TaxRates, so attempting to
create one resulted in the following exception:

```
TypeError: nil is not a symbol
xeroizer/lib/xeroizer/record/base.rb:52:in `[]'
xeroizer/lib/xeroizer/record/model_definition_helper.rb:88:in `id'
xeroizer/lib/xeroizer/record/base.rb:78:in `new_record?'
xeroizer/lib/xeroizer/record/base.rb:101:in `save'
```

This stemmed from being unable to query whether the TaxRate being
created was truly a `new_record?` or not.
Merge pull request #149 from tradegecko/oauth-header

Send the default headers in OAuth as well
Merge pull request #163 from chargify/tax_rates

Fixes Creation of TaxRates
updated gemspec for further oauth versions