Make grader accept different case columns

SELECT SUM(minutes) and SELECT sum(minutes) were not matching, but they should.

Test Plan:
- Do this challenge: /computer-programming/challenge-test-01/4703367146242048
- Complete the challenge using all lowercase.

Auditors: pamela
Remove spaces from column names when comparing

Consider the following:
SELECT SUM (minutes)
and
SELECT SUM(minutes)

SQLite names the columns differently because of the extra space after SUM.
We should normalize out spaces from column names when comparing.

Test Plan:
- Load /computing/hour-of-code/hour-of-sql/p/challenge-book-list-database
- Put a space after the SUM and make sure the code is accepted still.

Auditors: pamela
Fixes T3442 - bring up img picker for img src = ""

Test Plan:
- Run automated tests
- Create new webpage, type img src = "", see image picker pop up

Auditors: alexrodrigues
Adjusted the message to avoid using confusing 'block opener' / 'block closer' terminology

Test Plan:
- In new webpage in <style> tag:
- Type h2 { color: red, see message
- Type h2, see message

Auditors: alexrodrigues
Subscribers: #cs
Update build files.
Update structured-blocks with color/positioning fix and include positioning fix for toolbox

Test Plan:
- Load /computing/hour-of-code/hour-of-code-blocks/p/challenge-melting-snowman
- Be able to do the challenge step 1

Auditors: john

Subscribers: #cs
Update structured-blocks and build files.
Add dialog telling users to drag blocks from the toolbox to the editor to get started.
Add active state to number picker.