Rename currentEpoch to currentTimestamp - Not to be used interchangeably

[idiom-bytes]

Problem

An epoch is an index to a block of time epochs[1].timestamp.
A timestamp is a point in time (Sep 08 2021, 1631064675).

These are not the same type but are being used interchangeably in code. This doesn't read well when looking at old code, reviewing logic, or using it.

Example

DoD

• Please rename cEpoch and currentEpoch + inside PredictoorContext to be cTimestamp and currentTimestamp.
• Please review math and make sure it's working correctly.
• Please review if anything similar exists elsewhere and adjust

[KatunaNorbert]

If you try to get epoch from the contract it's going to return a timestamp

[kdetry]

let's do it currentEpochTimestamp because we do not get or set the real current timestamp (it is the value of the date.now() function). We set the timestamp of the current epoch