add character limits to schoolname and city/location

#### What's this PR do?
This adds a character limit of **CITY_SCHOOLNAME_CHARLIMIT** (currently set to 79 characters) to the combined sum of the location and schoolName properties of the donors choose proposal returned. 

This prevents the text message the user is opted into which contains this data from being longer than 160 characters. 

Additionally, there have been some formatting changes to the variables declared at the top of the `DonorsChooseDonationController.` 

#### Where should the reviewer start? 
Line 120 of the `DonorsChooseDonationsController.js`. 

#### How should this be manually tested?
Simple string manipulation, has been tested with a fake **selectedProposal** object. Can be tested again by using [this REPL tool](http://repl.it/0wk) (code saved.) 

#### What are the relevant tickets?
JIRA SMS-99