Include guards are not consistently named

[confluence]

The #ifndef guards in our headers and template files are inconsistently named -- some still reflect old file names or locations, some never used the same convention in the first place, etc.. It would be simple to extend our style.py script to check and fix these automatically.

Here's a discussion of various possible naming conventions. My suggestion would be something like CARTA_PATH_TO_FILE_H_, which is close to what we have already. Maybe with the top-level directory included, so that we can distinguish between CARTA_SRC... and CARTA_TEST... ?

[confluence]

I think a sensible convention would be CARTA_SRC_... for everything in src, and CARTA_TEST_... for everything in test. The BACKEND is redundant and should be removed. After that, the name should follow the path.

Examples:

• src/HttpServer/HttpServer.h: CARTA_SRC_HTTPSERVER_HTTPSERVER_H_
• src/Cache/RequirementsCache.h: CARTA_SRC_CACHE_REQUIREMENTSCACHE_H_
• test/CommonTestUtilities.h: CARTA_TEST_COMMONTESTUTILITIES_H_

It should be possible to do this automatically with a bash script. It's also relatively low-priority (purely cosmetic).