removed tabs in stan and test files

#### Summary:
Removes tabs in all of src/stan and src/test files. (issue #696)

#### Intended Effect:
Removed tabs.

#### How to Verify:
See files changed and run 
```
grep -R "\t" src/stan 
```
```
grep -R "\t" src/test 
```

#### Side Effects:
None.

#### Documentation:
None.

#### Reviewer Suggestions:
Anyone.