Fix various minor typos, grammatical errors, and awkward phrasing in code comments and docstrings across the codebase:
- miner.cpp: Fix 'different then' to 'different from'.
- coinselection.h: Fix 'less then' in docstring comment.
- httpserver.h: Use 'a unique id' instead of 'an unique id'.
- txgraph.cpp & txgraph_tests.cpp: Fix 'an transaction', typo 'top the back' -> 'to the back', and compound 'everytime'.
- log_raw_p2p_msgs.py: Remove duplicated word 'that that'.
- pcp.cpp: Improve response error comment phrasing.
- blockchain.cpp: Improve 'allow to abort' and pluralize 'every 256 item'.
- rpcconsole.cpp & walletview.cpp: Improve phrasing to use gerunds and clearer clauses.
- fees.cpp: Improve 'Allow to override... over' to 'Allow overriding... on'.
- bloom_tests.cpp & parse_numbers.cpp: Add missing apostrophes ('Don't', 'it's').