Was bugging the response when enabled

- Add proper error handling in libs/db/query_exec. Uses a catch function after each then to proper capture database errors and report them to the user.
- Add logging the error stack when a database query error occurs.
- Change error message reported in the response when a database query occurs, because the person making the request does not need to know about an internal error in the database.

Signed-off-by: João Victor Tozatti Risso <jvtr12@inf.ufpr.br>

This reverts commit bfe64623, reversing
changes made to 9c8cfa58.

Changes:
* Cache is defined in `api.js`, not in `app.js` anymore
* Enrollment cache lasts for 1 day, states, regions, citys and schools lastas for 15 days

Closes simcaq/SCRUM#58

Related: simcaq/SCRUM#18

Also the req.sql attribute is being created ("injected") before all routes

Related: simcaq/SCRUM#18

Changing apps to follow suggested practices from documentation
and centralizing prefix /api/v1 in the app module.

Cache lasts for a day

Changes in this commit:
- Singularize all routes and components
- Separate different modules into their own source files
- Rename the API module to enrollment and add a more general API module
- Resources that are related to a route, are now under its scope. For
  example, the year range of the enrollment component is now under the
  route /v1/enrollment/year_range
- Implement a thenable function to execute the queries against the
  database to reduce the amount of duplicated code in the application. This
  approach also allows several concurrent queries to run concurrently in the
  same route.

Major modifications:
- Source code is now in the src directory
- All source files were adapted to ECMAScript6
- Add Gulpfile and Babel to transcompile the project from ES6 to ES5 (until Node.js fully supports ES6)
	- By running gulp one generates the build directory with the files transcompiled, from which the API can be run
- Add ESLint to check for syntax errors and enforce code standards
	- Javascript coding standard currently adopted is AirBnB with 4 spaces
- Replace monetdb package with monetdb-pool, which allows for concurrent queries over a pool of connections while maintaining the same interface

TODO (in order of priority, from high to low):
- Add Gulp tasks to handle automatic building, tests and running the server in order to deprecate using npm
- Implement decorator to execute the SQL queries and reduce code duplication.
- Implement SQL query builder (e.g. squel.js) to erradicate the need for embedding SQL directly into the code (which is error-prone).
- Change enrollments route not to use route chaining in order to decide which SQL query is appropriate to respond the user's request.
- Implement decorator for API responses and also reduce code duplication.
- Split up tests into and add more test cases.

Signed-off-by: João Victor Risso <jvtr12@c3sl.ufpr.br>