Remove then branch of always false condition

Summary: The condition in `OctaveExpresssion::parseError` never comes `true`, so remove `then` branch.

Reviewers: #cantor, asemke

Reviewed By: #cantor, asemke

Subscribers: #kde_edu, #cantor

Tags: #cantor, #kde_edu

Differential Revision: https://phabricator.kde.org/D11965

Add amsmath package to LaTeX template

Summary: `amsmath` package widely spread and has useful funcitons, the existence of which user expects from LaTeX entry.

Reviewers: #cantor, asemke

Reviewed By: #cantor, asemke

Subscribers: #cantor, #kde_edu

Tags: #kde_edu, #cantor

Differential Revision: https://phabricator.kde.org/D11994

Added couple of missing variable initialisations and override keywords.

Add forgotten print command `plot3` to octavebackend print commands.

Summary: This command missing, so cantor don't show plot result of this command. This change fix it.

Reviewers: #cantor, asemke

Subscribers: #cantor, #kde_edu

Tags: #kde_edu, #cantor

Differential Revision: https://phabricator.kde.org/D12022

[Octave] add couple of more 3d plot commands.

[Octave] added couple of missing 2d plot commands.

Fix bad performance for `addRules` in `DefaultHighlighter` for big containers

Summary: Now, in `addRules` we call `addRule`, which emit `rulesChanged`, that leads to `rehighlight` all worksheet. This is useless work, because for each rule in rules container we reprocessing all worksheet. (instead better option to emit `rulesChanged` only one time after container processing). So, when container is big, performance falls quite strongly, for example highlighter of octave backend spends 2-4 seconds for adding new function. So this changes improve `emit` logic, calling only one event for rules container.

Test Plan:
1) Start octave backend, write octave function, check, that cantor is freezed for few seconds
2) Apply patch
3) Check, that octave backend don't freeze after entry with user function.

Reviewers: #cantor, asemke

Subscribers: #cantor, #kde_edu

Tags: #kde_edu, #cantor

Differential Revision: https://phabricator.kde.org/D11992

Show waiting cursor while openning a project.

Small improving of order of logic operators in evaluateNext

Reviewers: #cantor, asemke

Subscribers: #cantor, #kde_edu

Tags: #kde_edu, #cantor

Differential Revision: https://phabricator.kde.org/D12018

Add parsing errors in lua backend

Summary: Luabackend haven't parsed errors, so if entries cause errors, we just get empty output (but not empty error output, which don't check). This add error handling, so now we could see, if errors hapened.

Test Plan:
1) Start lua session, and check, that wrong lua expression don't produce any output.
2) Apply this patch
3) Check, that how wrong lua expression produce output and cause error entry status

Reviewers: #cantor, asemke

Subscribers: #cantor, #kde_edu

Tags: #kde_edu, #cantor

Differential Revision: https://phabricator.kde.org/D11963