Rename entities across the docs

[novusnota]

For simplicity, clarity, and, in some regard, conformance to grammar.ohm, I propose renaming of many terms throughout the docs.

Changes:

• global static functions -> global functions
• internal functions -> storage functions
• persistent state variables -> storage variables
• constants: global and storage ones
• getter functions: off-chain functions / accessors (preserve the older "getter" name alongside the new one too)
• describe that maps are called dicts or dictionaries in FunC, Fift, TVM and various bindings, such that the page about them is easier to find for newcomers from FunC ("dictionaries: hashmap -> map" transition).

Potential changes (not sure):

• serialization types → storage specifiers/modifiers (especially on book/integers page)

[novusnota]

Also: #374, with "mutating" or "mutation" being the correct choice over "mutable"