Reduce the duplicate code in IK and TSID

[GiulioRomualdi]

This PR tries to reduce the duplicate code in IK and TSID and implements what has been discussed in #363.

I implemented the ILinearTaskSolver interface from which TSID and IK inherit. I also implemented TSIDLinearTask and IKLinearTask that are two specializations of LinearTask. Each IK task will inherit from IKLinearTask while each TSID task from TSIDLinearTask.

No actions are required by the user to adapt the consumer libraries to this new implementation.

cc @traversaro @isorrentino @S-Dafarra @paolo-viceconte

[S-Dafarra]

What is your plan for IKLinearTask and TSIDLinearTask? At the moment they simply inherit from LinearTask, so I was wondering why not using LinearTask directly. Are you planning to add new methods in the future?

[GiulioRomualdi]

The idea is to avoid that someone uses a IK task in TSID and viceversa

[S-Dafarra]

The idea is to avoid that someone uses a IK task in TSID and viceversa

Ah, I see. I also see why you used the template then, nice!

[S-Dafarra]

The macOS job failed with error

2021-07-12T11:15:39.5015400Z Can't find any online and idle self-hosted or hosted runner in the current repository, account/organization that matches the required labels: 'macOS-latest'
2021-07-12T11:15:39.5015541Z Found online and busy hosted runner(s) in the current repository's organization account that matches the required labels: 'macOS-latest'. Hit concurrency limits on the hosted runners. Waiting for one of them to get assigned for this job.
2021-07-12T11:15:39.5015572Z Waiting for a hosted runner in 'organization' to pick this job...

Maybe it should be macos-latest (with the lowercase o) in https://github.com/dic-iit/bipedal-locomotion-framework/blob/master/.github/workflows/ci.yml#L55 instead (see https://docs.github.com/en/actions/using-github-hosted-runners/about-github-hosted-runners)?