This should help with proper HEAD label display in the table: even for expanded groups, HEAD reference should not be shown in the list, yet the group still has to have a yellow tag.
Also, SimpleRefGroup class from Mercurial plugin is extracted and moved to the vcs-log impl. This class now can be used from git and mercurial, and it has a proper getColors method moved from LabelPainter.

Introduce vcs.log.labels.left.aligned. It keeps labels design, but shifts them to the left.

* add Nullable annotations for editor parameter;
* check if null in HtmlFileDropHandler;

Remove modification flag and listeners from fields because use of them makes Apply button always active even no real changes was made

Refactor settings creation: 1) Erase password on login change 2) Do not erase password on focus gained by password field 3) Use lambda instead of anonymous class where possible

Refactor stepik settings: 1) Login in settings under progress  2) Do not save new credentials until they are posted on stepic 3) Remove default password for show: set user password in stepik settings panel

Java: Created an inspection (with a quick fix) that checks if a package is exported to the same module where it's declared. Tests added. (IDEA-164129)