Fix etrago_id conflicts

[ClaraBuettner]

To avoid conflicts with using the same index for eTraGo tables, eMobilit currently has many dependencies.
But the problem should be fixed differently (see openego#927)
By then, the dependencies for eMobility should be removed. These were added in this commit: openego@a0d3db3

Options to fix this problem

• reserve and store ids in seperate sequence
• write data into intermediate tables
• use combination of carrier and index as id