Update Appveyor build dependencies

dcmqi is using pre-built binaries of ITK and DCMTK for Appveyor to reduce the overall build time of the library.

Every time the release of DCMTK/ITK needs to be updated, it is important to re-generate these binaries, otherwise Appveyor build will fail when there are API changes.

Updating DCMTK and ITK packages

The modified version of DCMTK is located in the dcmqi branch of the dcmtk-dcmqi repository. The only difference from the stock DCMTK source code is the appveyor.yml file. Thus, the steps are the following:

1. Check out the version of DCMTK that needs to be used

2. Rebase the dcmqi branch of dcmtk-dcmqi to the new version.

3. Update the name of the package to reflect the version and date of the DCMTK package to be created (deploy/release section of the appveyor.yml)

4. Push the updated dcmqi branch to QIICR/dcmtk-dcmqi

Appveyor build will be triggered automatically, and barring any build issues a new release will be uploaded to https://github.com/QIICR/dcmtk-dcmqi/releases.

The URL corresponding to DCMTK-dcmqi.zip in the release should then be used to first update https://github.com/QIICR/ITK-dcmqi/blob/dcmqi/appveyor.yml, which should result in re-generated ITK-dcmqi package under ITK-dcmqi releases in https://github.com/QIICR/ITK-dcmqi/releases. At that time, URLs for both ITK-dcmqi and DCMTK-dcmqi packages should be updated in the dcmqi appveyor script file: https://github.com/QIICR/dcmqi/blob/master/appveyor.yml.