Adding GetPixelID method to image class.

This is the intended replacement for the GetPixelIDValue method as it
returns an enumerated type as opposed to an integer.

Updated PimpleImageBase to use PixelID enum where it can.

Change-Id: I13df278b4b0958411e3c2bb7b9ae1773e0c7c4f3
Updating tests to prefer GetPixelID

Change-Id: I2632780e15f3aed9b00a09c639de5ac7f07d1040
ImageSource filters now that PixelID enum for type.

Change-Id: I3a7e0222fbb922ecdf7f8cc95409febf247c7c9a
Internally prefer PixelIDValueEnum in ExecuteInternal method.

Change-Id: Ibd79df78d4dec203fb52af43290194f73d228551
Updating GetPixelIDValueAsString to additionally take enum.

Change-Id: I5f03a29cf3a8cbc31f81d184f470755f230a372f
fixup for testing changes

Change-Id: I8b95ba1676f0983114dce3d8f8b2fef8b2ddb599
Prefer PixelID enum in internal Execute method

Change-Id: I10e34da2adeb5a3b2c24b0661e2de46b20c5a039
Adding additional method to CastImageFilter for PixelID enum.

Update example to use preferred PixelID enum methods.

Change-Id: I7b6cac4e72b06c6557a19720eb67cd966f1ae34a
ignore overloaded PixelID methods where conflict occurs in SWIG.

For the wrapped languages where are not strongly typed the int and the
pseudo enum type are the same, causing a conflict for this overloaded
method. So, these languages ignore the int overloaded methods.

BUG: adding missing Ruby.i SWIG customization file

Change-Id: I95f1f851ba0849ef11a36bcb7e40a4401be76736
R now is requiring that enum be passed as strings

Updated tests to use pixel ID as strings.

This is not ideal, it would be better if there were variables with
predefined values which had the correct value to use as enums. this
would help with tab completion.

Change-Id: If3c9f939699649b8da06d048a0dcd2866879e460
Merge topic 'SIMPLEITK-294_UsePixelIDValueEnum'

fb7a48b R now is requiring that enum be passed as strings
dccac35 ignore overloaded PixelID methods where conflict occurs in SWIG.
5a1c623 Adding additional method to CastImageFilter for PixelID enum.
455e12a Prefer PixelID enum in internal Execute method
9d7e720 fixup for testing changes
8a11ac0 Updating GetPixelIDValueAsString to additionally take enum.
334ee2c Internally prefer PixelIDValueEnum in ExecuteInternal method.
f2840cf ImageSource filters now that PixelID enum for type.
6429fc1 Updating tests to prefer GetPixelID
da5d381 Adding GetPixelID method to image class.