Create a NimbusDatabase function to handle statistical/aggregation questions

## Objective
Create a NimbusDatabase function to handle statistical/aggregation questions like the following...
**How many sections of CSC 480 are offered this quarter?**
**How many teachers are interested in Artificial Intelligence?**

Examples of _aggregations_
* **total count** ("how many of X?")
* **unique count** ("how many kinds of X?")
* **date range** ("Between what times does X happen?")
* **earliest date** ("When is the earliest section of COURSE?")
* **latest date** ("When is the latest section of COURSE?")
* **boolean count** (total count true / total count false) ("How often is X true?")
* **boolean satisfiability** ("Is X always true?")

## Key Result
Commit code to the `NimbusMySQLAlchemy` class in `database_wrapper.py` that can generally answer any aggregation question

## Details

### **Relevant Code**
#### How many courses are there in the database? = 178
```
>>> from database_wrapper import NimbusMySQLAlchemy
>>> db = NimbusMySQLAlchemy()
initialized database session
initialized NimbusMySQLAlchemy
NimbusMySQLAlchemy closed
>>> db.session.query(db.Courses).count()
178
```

#### How many UNIQUE courses are there in the database? = 178
```
>>> from database_wrapper import NimbusMySQLAlchemy
>>> db = NimbusMySQLAlchemy()
initialized database session
initialized NimbusMySQLAlchemy
NimbusMySQLAlchemy closed
>>> db.session.query(db.Courses).distinct().count()
178
```

#### What is the `deptartment, courseNum, units` of any course with the most units?
```
>>> db.session.query(db.Courses.dept).add_column(db.Courses.courseNum).add_column(db.Courses.units).distinct().order_by(db.Courses.units.desc()).first()
('CPE', 494, '6')
```

#### What is the `deptartment, courseNum, units` of any course with the least units?
```
>>> db.session.query(db.Courses.dept).add_column(db.Courses.courseNum).add_column(db.Courses.units).distinct().order_by(db.Courses.units.asc()).first()
('CPE', 100, '1')
```

#### What are the CSC480 sections?
```
>>> db.session.query(db.Sections.section_name).add_column(db.Sections.instructor).filter(db.Sections.section_name.contains("480")).all()
[('CSC 480_06', 'Kauffman, Daniel Alexander')]
```

#### How many?
```
>>> db.session.query(db.Sections.section_name).add_column(db.Sections.instructor).filter(db.Sections.section_name.contains("480")).count()
1
```