add DELETE options for _alias

Several aliases can be deleted at once by defining several indices and names with

`[DELETE] /{index}/_alias/{type}`

where

`index= * | _all | glob pattern | name1, name2, …`

`type= * | _all | glob pattern | name1, name2, …`

Alternatively, the keyword `_aliases` can be used.

see roadmap at issue #4071