This commit introduces `MIN_LOCKUP_PERIOD` and `MAX_LOCKUP_PERIOD` and
makes use of them within `StakeManager.stake()` and
`StakeManager.lock()` accordingly.
When users deposit tokens into their vault via `stake()`, they can
provide an optional lockup time. If the value is `0` it implies users do
not want to lock their stake.
If the value is `> 0` it has to be within the range of
`MIN_LOCKUP_PERIOD` and `MAX_LOCKUP_PERIOD`.
Properly addresses #15
This commit introduces a first version of a `VaultFactory` that later
will be extended to be capable of instantiating reward vaults and
possible keep track of vault instances per owner.
As a first step, this implementation comes with a `createVault()`
function which takes care of creating vaults.
Because `VaultFactory` also knows about `StakeManager` it can derive the
manager's address and stake token from it when creating vaults, allowing
the API to be without arguments.
Partially addresses #37
Because the `stakedToken` property is `immutable`, solhint recommends to
make it in all caps. This commit changes the property to adhere to that
rule and also makes the property private.
To access the `stakedToken` there's now a `stakedToken()` function on
the contract.
r4bbit