Adds a validator, invoked through `fission spec validate` and before `fission spec apply`. The validator checks for duplicate names, dangling references, and unused resources.
Also attempts to fix a race between CLI and builder. Avoids replacing a package while it's building, instead waiting for the build status to change from pending before updating it.
The cli spec dir flag name should be `specdir`, not `specs`, that should match to:
```go
specDirFlag := cli.StringFlag{Name: "specdir", Usage: "Directory to store specs, defaults to ./specs"}
```
in fission/main.go
Currently it cause the specific specs dir not to work.
```
$ fission spec apply --specdir <my spec dir>
Everything up to date.
```
This change enables users to have declarative specifications for Fission resources. Users can specify their "app" in a set of spec files, and use a new fission CLI command to "apply" these specs to a running cluster.
The new "spec" CLI also includes archiving of local source files, and a file watcher that re-builds archives and uploads them on file changes, and a package build watcher that waits for package builds on the CLI.
A "--spec" option is also added to "function create", and will be added to other resources in future changes. This option causes a YAML to be outputted to the specs directory instead of the resource being created on the cluster.
The CLI "fission spec --help" outputs usage information.
