Merge RecoEgamma/Egamma{Electron,Photon,Isolation}Algos

This merges:

- `RecoEgamma/EgammaElectronAlgos`
- `RecoEgamma/EgammaPhotonAlgos`
- `RecoEgamma/EgammaIsolationAlgos`

into `RecoEgamma/EgammaAlgos`.

The excuse for this is trying to reduce the number of libraries which use TLS, in the end it's probably a good idea to do it anyways. The new libraries for `RecoEgamma/EgammaAlgos` are 20% smaller than the sum of the libraries of the other package.