move database essentials to python labs

Not an algorithm, but more of a Python lab anyway.
fix small typo in sql solutions
add sql labs to vol3
remove erroneous character
Lab: Advanced SQL

Cover advanced topic in SQL databases.  A successor to the SQL lab.
modify db table.
new color scheme

created a formal color scheme instead of almost random colors.
add extra column to latex table
add space in code boxes.
add subsection about group by and order by

Finish joins.
add problem for group by and order by.
add case expressions

Describe simple and searched case expressions in SQL expressions.
modify hyperref to underline links

Underline hyperlinks instead of drawing a frame around them.
add final problem

add labels to each problem to identify their solutions.
solutions for advanced sql problems
add problem for LIKE keyword
removed unnecessary custom colors
Merge pull request #571 from ayr0/links

Underline links
modify colors again.
Merge branch 'develop' into colors