Add limited 'global statement' functionality (inefficient)

[kevinsogo]

No changes to the DB were made here, so I had to use a hacky way of checking whether there is a global statement: Literally check that all tasks have exactly the same .pdf statements!

Luckily, CMS already caches files, so if two files are exactly the same, then they are stored as the same file object in the DB, and we can just compare digests instead of the full files.

Note that there's some inefficiency here since many requests will now call the get_global_statements function which fetches several objects from the DB just to compute whether there's a global statement.

[kevinsogo]

Please "Squash and merge" this when you merge. Thanks

[kevinsogo]

When you merge this, please merge the "noi" branch into the "noitama" branch. Thanks

[kevinsogo]

Okay after discussion with @jabbawookiees , I initially considered adding caching to get_global_statements, pero tingin ko wag na. I'm planning on overhauling this naman by Abakoda with a more proper implementation that actually touches the DB. Maganda na rin itong trial run to know how well the server will be able to handle the TAMa load, haha