Add support for image orientation

[TheZ3ro]

Fixes #540

Modern image formats (PNG, JPEG, Tiff, etc) embed the orientation in Exif metadata.
When rotating or displaying an image, software like Word, PowerPoint, macOS Preview, Android Google Photo, etc do not rotate the actual pixel data but instead change the orientation metadata integer (https://exifstrip.com/guides/orientation-tag-explained)

This is governed in OpenXML with the a:xfrm (transform) tag. This tag can contain the rot, flipV, and flipH attributes. By mapping the 1-8 orientation values to the respective rot and flip attributes it's possible to display images that were rotated by merely changing the Exif metadata with the correct orientation.

This PR add support for image orientation.

By default it gets orientation from Exif metadata. If orientation metadata is not available it falls back to "Normal" orientation (like now, defined by raw pixel data).

It is also possible to force a given orientation programmatically by:

document.add_picture(path_to_picture, width=Inches(3), orientation=EXIF_ORIENTATION.ROTATE_90))
last_paragraph = document.paragraphs[-1]
last_paragraph.alignment = WD_ALIGN_PARAGRAPH.CENTER

[TheZ3ro]

script to reproduce/test the behavior:

from docx import Document
from PIL import Image, ImageDraw

# Draw a black arrow shaft and arrowhead
img = Image.new("RGB", (300, 400), "white")
d = ImageDraw.Draw(img)
cx, shaft_top, shaft_h = 150, 50, 200
d.rectangle([(145, shaft_top), (155, shaft_top + shaft_h)], fill="black")
d.polygon([(150, 30), (130, 70), (170, 70)], fill="black")
# Save the image
img.save("arrow.jpg")

# Create a document and add the image
document = Document()
document.add_picture("arrow.jpg")
document.save("arrow_up.docx")

# Rotate the image only by changing the EXIF orientation, then save it
img = Image.open("arrow.jpg")
exif = img.getexif()
exif[0x0112] = 6
img.save("arrow_rotated.jpg", exif=exif)

# Create a document and add the rotated image
document = Document()
document.add_picture("arrow_rotated.jpg")
document.save("arrow_rotated.docx")