Simplify the code in "On the Job Search"

[jlperla]

https://julia.quantecon.org/dynamic_programming/jv.html

Even after the merging of #352 there is some improvement to be done.

• one thing, the T! has overloads, which are confusing and require type annotations. We are better off just renaming the second usage and removing the type annotations
• In Julia the convention is that in-plcae functions modify the first argument, so T! should follow that approach.
• The "search grid" approach might be cleaner if done with some sort of optimization or just broadcasting with a max
• The "ifelse" at the bottom is tough to understand

I suspect there will be a few other improvements worth doing.