Merge pull request #384 from pburdet/BUG_add_Lines

Bug add lines
Merge pull request #385 from pburdet/EHN_elements_database_add_Xray_lines

Ehn elements database add xray lines
Merge pull request #377 from francisco-dlp/FIX_tests_fails_round_off_error

Fix tests fails round off error
BUG-FIX: add check in _get_component to check if component is in the model

Fixes confusing expection when m.fit_component is called with a
component which is not in the model.
Fix wrong indention in m._get_component
Add test: checking if component is in model when using m.fit_component
Merge remote-tracking branch 'magnus/ENH_check_if_component_is_in_model' into 0.7.x