[QA] Update desktop client test plan with the test suites in TestRail

[saw-jan]

JIRA: ??? (Desktop Client)

Testrail test suites: test-cases-from-testrail.csv

Update and reorganise the desktop test plan folder: https://github.com/owncloud/QA/tree/master/Desktop
💡 We can move the existing files and folders to a folder: old-test-plans or something similar and add the new test plans