Standardize legal headers and LICENSE.md

[deepyaman]

Description

legal_header.txt (and the corresponding legal headers on top of source files) has nonstandard indentation on line 22 (middle line below):

# Trademarks or any confusingly similar mark as a trademark for your product,
#     or use the QuantumBlack Trademarks in any other manner that might cause
# confusion in the marketplace, including but not limited to in advertising,

Upon further investigation, this line isn't indented in LICENSE.md, but the Apache link is: https://github.com/quantumblacklabs/kedro/blob/d2d5ca1804d8a5b1d4ea2fe67ac09732e92956dc/LICENSE.md#L7

Context

Why is this change important to you? How would you use it? How can it benefit other users?

Other users can sleep easy at night, no longer haunted by the fact that a random line is over-indented.

Issue also applies to https://github.com/quantumblacklabs/kedro-viz, https://github.com/quantumblacklabs/causalnex, etc.

Possible Implementation

See #365

Possible Alternatives

You can still keep legal_header.txt, if you foresee it diverging from LICENSE.md in the near future. I'd prefer to add it back later, if and when necessary, though.

[921kiyo]

Resolved in 648f894 Thank you for your contribution!