Add script for creating docker images. Refactor handling.

[dnouri]

• Refactor docker base image and update docs.
• Upload base image to docker hub.
• Refactor docker add app image and update docs.
• Allow docker app image to be created through a more convenient command-line script.

[coveralls]

Coverage remained the same at 100.0% when pulling 6c23147 on GBIPMMF-190 into 6805789 on develop.

[coveralls]

Coverage remained the same at 100.0% when pulling 93a9793 on GBIPMMF-190 into 6805789 on develop.

[dnouri]

@alattner Could you please proof-read the docs changes in the last commit? There's also another comment in there.

Also, do we already have a Docker hub account? Assume not, in which case I'll probably just create ottogroup?

[coveralls]

Coverage remained the same at 100.0% when pulling 77fd7ed on GBIPMMF-190 into 6805789 on develop.

[coveralls]

Coverage remained the same at 100.0% when pulling 57db018 on GBIPMMF-190 into 6805789 on develop.

[coveralls]

Coverage remained the same at 100.0% when pulling 37c01b2 on GBIPMMF-190 into 6805789 on develop.

[coveralls]

Coverage remained the same at 100.0% when pulling 5399536 on GBIPMMF-190 into 6805789 on develop.

[coveralls]

Coverage remained the same at 100.0% when pulling 09ba3ec on GBIPMMF-190 into 6805789 on develop.