A lot of small fixes in tools.common

- Fixed time list generation in tools.common.get_e0;
- Cleared unneeded read_ini calls;
- Added output of E_0 only at the end of modelling;
- Updated docstrings in tools.common;
- Common functions now output list of r's, not z's;
- Changed arguments for cell_z and cell_r;
- Updated write_text_output, now can accept arbitary number of data series.