Added property uid to column

[vinagreti]

What kind of change does this PR introduce? (check one with "x")

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior? (You can also link to an open issue here)
When we receive a click event, the column data does not give us a way to distinguish between the columns.
We have prop (that enables sort), we have label but both of them are displayed at the column title.
The problem here is that if we create columns without label and prop is not possible to distinguish each one of them.
The reason to do not use label/prop is that if we do we end up enabling sort or displaying the title and we want to use multiple empty column headers.

Even using the column index is not sufficient because in dynamic tables (where we can hide columns, add others) we'll end up with different indexes depending of the number of columns that are visible in the specific time.

What is the new behavior?
Added @Input() uid: string to the column component enabling us to distinguish one column from each other.

Does this PR introduce a breaking change? (check one with "x")

• Yes
• No

If this PR contains a breaking change, please describe the impact and migration path for existing applications: ...

Other information:
I've tested and it seems to be ok. Also, I used lint to trim spaces.