AP-589: rebuild image based on iipsrv 1.3

[anarchivist]

Ruven, the IIPImage maintainer, updates the iipsrv images upon new releases of iipsrv. This PR uses his (Alpine/lighttpd-based) image as a base image and update the package dependencies as part of the build process.

This upgrades us from IIPImage 1.1 to 1.3. One of the major changes in 1.2 is that iipsrv now supports the version 3.0 of the IIIF Image API, which necessitates some changes in the fixtures we're using. Otherwise, IIPImage 1.3 should be a drop-in replacement for the v1.1 image we have been using for UCBEARS.

[anarchivist]

@danschmidt5189 this is ready for re-review. tldr:

• this updates the image to build iipsrv 1.3, and provides a parameterized build to allow us to compile other branches/tags as needed.
• iipsrv 1.2+ returns iiif image api v3 responses by default. the tests and readme have been updated to reflect htis.
• at some point debian libtiff-dev introduced libwebp-dev as a dependency; accordingly, autoconf detects it and builds webp support into iipsrv by default. this introduces a runtime dependency on libwebpmux3, which is added to the base image deps. we could certainly disable webp support, but i don't think it's worth it.
• finally: UCBEARS tests are passing with the image built from this branch.

[awilfox]

Looks good to me, but I'm not sure if we want to document IIPSRV_VERSION specifically in the README.

r+ otherwise.

[anarchivist]

@awilfox thanks; that's been fixed in 64ce4c1.

[danschmidt5189]

Looks good! 🚢