[lp_intro] Editorial Suggestions

Comments by @longye-tian.

[x] Unbold non-definition words and use italics for emphases
[x] Remove capitalization in the titles
[x] Add period for the first sentence in example 1
[x] Unbold column name in the table
[x] Define $z$ as revenue
[x] Remove the grid in the figure
[x] #476
[x] use "ortools.linear_solver"
[x] "... using it's status" -> "... using its status"
[x] Round the print in the format string for printing.
[x] "three year" -> "three-year"
[x] Add scipy version for the first example and create some comparison
[x] "Let's us" -> "Let's"
[x] "LP" -> "Linear programming"
[x] In the dot point in the "useful transformations" section, remove the capitalization of the second word.
[x] Migrate all the theories and concepts before examples? (@jstac)
[x] Explain notations for $A_eq$ and $A_ub$.
[x] 'bounds' -> bounds
[x] Add an exercise using scipy.
[x] Consider if the standard form needs to be removed as we are doing proofs in this lecture (@jstac).
[x] We did not discuss complementary slackness, so we can delete it.

QuantEcon / lecture-python-intro