check for column-names uniqueness added

Currently, you can do:
```Clojure
user=> (dataset [:c :c] [[1 2 3] [4 5 6]])
#clojure.core.matrix.impl.dataset.DataSet{:column-names [:c :c], :columns [[1 2 3] [4 5 6]]}
```
After PR:
```Clojure
user=> (dataset [:c :c] [[1 2 3] [4 5 6]])
RuntimeException DataSet does not support duplicate column names  clojure.core.matrix.impl.dataset/construct-dataset (dataset.clj:21)
```