Ability to disable indentation

[JuanLucha]

The indentation was changed in a previous PR, but that PR removed the ability to disable the indentation.

You only has to put the next lines on the indent/typescript.vim file, on line 4:

if get(g:, 'typescript_indent_disable')
   finish
endif

Thanks for your work with this plugin.

[leafgarland]

I would like to use the indent in https://github.com/pangloss/vim-javascript, with only small changes to work with the typescript filetype. If it does not have a toggle, that looks like a small enough change to add.