added project importer and grandtotal converter

[kevinpapst]

Description

• Restructured importer for better code extensions
• Added a GrandTotal customer importer
• Added a real project importer
• Added a pure customer importer

TODO:

• add tests
• write documentation - see https://www.kimai.org/documentation/imports.html

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I verified that my code applies to the guidelines (composer kimai:code-check)
• I updated the documentation (see here)
• I agree that this code is used in Kimai and will be published under the MIT license

[codecov]

Codecov Report

Merging #1468 into master will increase coverage by 0.14%.
The diff coverage is 98.01%.

@@             Coverage Diff              @@
##             master    #1468      +/-   ##
============================================
+ Coverage     93.30%   93.44%   +0.14%     
- Complexity     5472     5747     +275     
============================================
  Files           518      530      +12     
  Lines         16808    17457     +649     
============================================
+ Hits          15682    16313     +631     
- Misses         1126     1144      +18     

Impacted Files	Coverage Δ	Complexity Δ
src/Configuration/FormConfiguration.php	100.00% <ø> (ø)	11.00 <0.00> (ø)
src/Importer/AbstractCustomerImporter.php	94.87% <94.87%> (ø)	22.00 <22.00> (?)
src/Command/ImportProjectCommand.php	94.91% <94.91%> (ø)	26.00 <26.00> (?)
src/Command/ImportCustomerCommand.php	94.93% <95.45%> (ø)	17.00 <1.00> (?)
src/Importer/AbstractProjectImporter.php	98.30% <98.30%> (ø)	29.00 <29.00> (?)
src/Importer/GrandtotalCustomerImporter.php	98.94% <98.94%> (ø)	55.00 <55.00> (?)
src/API/UserController.php	100.00% <100.00%> (ø)	16.00 <1.00> (ø)
src/Configuration/SystemConfiguration.php	100.00% <100.00%> (ø)	26.00 <10.00> (+10.00)
src/Controller/ActivityController.php	91.42% <100.00%> (ø)	42.00 <1.00> (ø)
src/Controller/CustomerController.php	91.24% <100.00%> (ø)	52.00 <2.00> (ø)
... and 27 more