Fix #357 - Allow passing integers as arguments to graphql.Time parameters

[MaxInertia]

Read this for details: #357

TLDR version: This PR replaces this switch case in time.go

case int:
	t.Time = time.Unix(int64(input), 0)
	return nil

with this

case int32:
	t.Time = time.Unix(int64(input), 0)
	return nil
case int64:
	t.Time = time.Unix(input, 0)
	return nil

so we can pass integers as graphql.Time when the application is compiled for 64-bit architecture.

[pavelnikolov]

Can you, please, add some unit tests?