bug/265 - enable working hour function and issue/272 - new UI for setting page to work with working hour function

[brianzhang310]

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[brianzhang310]

A little summary

1. bug/265, added a TaskShifter class which re-writes the start-time and end-time of tasks to make sure every task is managed in working time
2. issue/272, made some changes on setting page. now, you can see there is a save button to save the changes in working hours. If users don't save changes or quit the setting page without saving it, the working hour won't be saved.

[brianzhang310]

@all-contributors please add @brianzhang310 for code, review, doc

[allcontributors[bot]]

@brianzhang310

I've put up a pull request to add @brianzhang310! :tada: