[#6] Fix issue 6 and partial refactor git.ts into file.service.ts and file.panel.component.ts

[YichenTang97]

Fixes #6, fixes #27, fixes #28, fixes #31, and a partial process of #81.

• Refactor displayModifiedFiles method in git.ts
• Display of the elements binded with template through file.panel.component.ts/html
• ""updateModifiedFiles"" method in file.service.ts called by file.panel.component.ts every 3 seconds to read git status
• file.panel.component.ts subscribes modifiedFiles (in the form of BehaviourSubject) in file.service.ts for status change
• select-all-checkbox binded with checked properties of modifiedFiles in file.panel.component.ts
• Modify addAndCommit method in git so that checked files are passed in, instead of having the method looking for checked files through DOM - which does not work anymore due to the use of (ngModel) for binding the checked properties of the checkboxes

Manual test steps:

Test one:

1. npm start
2. either sign in or continue without sign in
3. open a local repository
4. in the local repository, create a new text file
5. the new text file should show up no longer than 3 seconds in the file panel
6. without committing the change, delete the new file locally
7. the file should disappear from the file panel no later than 3 seconds, and the "Your modified files will appear here" placeholder should reappear

Test two:

1. repeat step 1 to 4 in test one
2. create another text file
3. both new files should show up no longer than 3 seconds in the file panel
4. click one of them to open diff panel for the file
5. remove the corresponding file locally
6. the corresponding file should disappear from file panel no later than after 3 seconds and the diff panel should be closed automatically

[YichenTang97]

Conflicts from #140. (import "bootstrap")

Fixed the conflictions in the new changes

[r4inee]

Also just a note, probably will be hard at this stage as the methods are quite big, but can add some tests with the service, maybe even as a separate PR considering the size.

[YichenTang97]

Also just a note, probably will be hard at this stage as the methods are quite big, but can add some tests with the service, maybe even as a separate PR considering the size.

Will be adding the tests in next PR.

[henryli333]

LGTM; will unblock once #142 is merged and this branch is tested on Windows :+1:

[YichenTang97]

Rebasing this branch to the latest master after #157 and #152......

[YichenTang97]

......Done

Tested against manual test steps in #157 and #152

Some changes are made from #157:

• The displayModifiedFiles function is completely removed from git.ts, and the onClick callback to the modified files divs are changed into toggleDiffPanel in file.service.ts.
• The changes made in the callback function (diffService.openFile) and in the formatNewFileLine function (element.innerText) are adapted correspondingly into file.service.ts.

[YichenTang97]

Merge conflicts fixed: adapted changes made in #162.