Resolve warnings for Staking and DAO smart contracts found by Slither

[matjazv]

What was the problem?

This PR resolves #69.

How was it solved?

• All important Slither warnings were resolved.

How was it tested?

Unit tests were modified accordingly to all changes.

Additional Information

One Low level warning was not resolved:

• uses timestamp for comparisons; Recommendation: Avoid relying on block.timestamp

One Informational level warning was not resolved:

• compares to a boolean constant; Recommendation: Remove the equality to the boolean constant.

Contracts are calculating todays day based on block.timestamp and in my opinion it's safe to use block.timestamp.
This recommendation would be valid if we'll be using block.timestamp for calculation of randomness. In this case block proposer could influence on block.timestamp and took his advantage on others.

For informational warning, it advises to instead of using:
require(isLockingPositionNull(lock) == false, "L2Staking: locking position does not exist");
we should use:
require(!isLockingPositionNull(lock), "L2Staking: locking position does not exist");
which is in my opinion more error prone than the first version.

[Phanco]

Is it intentional that some interfaces starts with capital I some with i?

[matjazv]

Is it intentional that some interfaces starts with capital I some with i?

Nice catch.
Only files which didn't exist before script was ran have capital I.
I've fixed the script and wrong file names.

[Phanco]

Thank you 👍