Use our uniq function if there is no uniq function.

# Problem
`uniq` function was introduced relatively new version of Vim, so we get the following error if there is no uniq function in older Vim:

```
Error detected while processing function projectlocal#apply:
line   11:
E117: Unknown function: uniq
E15: Invalid expression: uniq(sort(l:projectfile_filetypes))
E117: Unknown function: uniq
E15: Invalid expression: uniq(sort(l:projectfile_filetypes))
E117: Unknown function: uniq
```

# Solution
Add `projectlocal#uniq` function and use custom uniq function if we can't use uniq function in Vim.