Added three new index alias related apis.

Added apis to get specific index aliases based on filtering by alias name and index name:
```
curl -XGET 'localhost:9200/{index_or_alias}/_alias/{alias_name}'
```

Added delete index alias api for deleting a single index alias:
```
curl -XDELETE 'localhost:9200/{index}/_alias/{alias_name}'
```

Added create index alias api for adding a single index alias:
```
curl -XPUT 'localhost:9200/{index}/_alias/{alias_name}'

curl -XPUT 'localhost:9200/{index}/_alias/{alias_name}' -d '{
	"routing" : {routing},
	"filter" : {filter}
}'

```

Closes #3075 #3076 #3077